Praise be to Allah.

We can sum up the answer to this specious argument in the following points: 

Firstly: 

The hadeeth mentioned in the question is not proven from the Prophet (blessings and peace of Allah be upon him). It was narrated in a marfoo‘ report (i.e., attributed to the Prophet (blessings and peace of Allah be upon him) that Ibn ‘Abbaas (may Allah be pleased with him) said: 

When Ibraaheem the son of the Messenger of Allah (blessings and peace of Allah be upon him) died, the Messenger of Allah (blessings and peace of Allah be upon him) offered the funeral prayer for him and said: “He has a wet-nurse in Paradise, and if he had lived, he would have been a man of truth, a Prophet. If he had lived, his maternal uncles would have set the Egyptians set free, and no Egyptian would ever be enslaved.” 

This was narrated by Ibn Maajah in as-Sunan (1511) via Dawood ibn Shabeeb al-Baahili. He said: Ibraaheem ibn ‘Uthmaan told us: al-Hakam ibn ‘Utaybah told us, from Miqsam, from Ibn ‘Abbaas. 

This is a very weak (da‘eef jiddan) isnaad; there are two problems with it: 

The first problem is Ibraaheem ibn ‘Uthmaan, Abu Shaybah al-Kufi. The critics are unanimously agreed that he is da‘eef. He was classed as da‘eef by Ahmad and Ibn Ma‘een, and Ibn al-Mubaarak said concerning him: Cast him aside. At-Tirmidhi said: His hadeeth is odd. An-Nasaa’i said: His hadeeth is to be ignored. See: Tahdheeb at-Tahdheeb, 1/145. 

The second problem is the break in the isnaad. They said in the biography of Ibraaheem ibn ‘Uthmaan that he did not hear anything from al-Hakam except one hadeeth, but they did not mention this hadeeth. And they said in the biography of al-Hakam ibn ‘Utaybah that he did not hear anything from Miqsam except five hadeeths, of which this is not one; in addition to that, he was well known for tadlees (using vague words to give a wrong impression). See: Tahdheeb at-Tahdheeb, 2/434 

Hence Ibn ‘Adiyy classed this hadeeth as da‘eef in al-Kaamil (8/507), as did Ibn Hajar in al-Isaabah (1/94), Ibn Katheer in al-Bidaayah wa’n-Nihaayah (8/248, Dar Hijr edition), and as-Sakhkhaawi in al-Maqaasid al-Hasanah (p. 406). 

Shaykh al-Albaani (may Allah have mercy on him) said: 

This is a very weak isnaad (da‘eef jiddan). The hadeeth of this Ibraaheem is to be rejected. It was narrated by Ibn ‘Asaakir via Muhammad ibn Yoonus: Sa‘d ibn Aws Abu Zayd al-Ansaari told us: Baqiyyah told us, from him... This Baqiyah is mudallis (i.e., he used vague words to give a wrong impression, in this case narrating by saying ‘from’ instead of ‘I heard’ or the like). It is possible that he took it from this Ibraaheem or someone else who is dubious or not reliable, then he used vague words to give a false impression. 

Moreover, this isnaad also includes Muhammad ibn Yoonus – al-Kudaymi – who is a fabricator.

End quote from as-Silsilah ad-Da‘eefah (no. 3202; See also no. 220). 

The hadeeth has a corroborating report that was narrated by Ibn ‘Asaakir in Tareekh Dimashq (3/138) from Jaabir ibn ‘Abdullah (may Allah be pleased with him), a marfoo‘ report (i.e., attributed to the Prophet (blessings and peace of Allah be upon him)): “If Ibraaheem had lived, he would have been a Prophet.” However this report is also very weak (da‘eef jiddan). Its isnaad includes Thaabit ibn Abi Safiyyah, Abu Hamzah al-Thamaali, of whom Imam Ahmad said: He is da‘eef; he is nothing. Abu Haatim and Abu Zar‘ah said: He is layyin al-hadeeth (a kind of weak narrator). An-Nasaa’i said: He is not trustworthy. Ibn ‘Adiyy said: His weakness is clear from his reports, and he is more likely to be weak. Ibn Hibbaan said: He often confused in his narration, to such an extent that he cannot be quoted as evidence if he is the only narrator of a report, in addition to the fact that he was extreme in his Shi‘ism. See: Tahdheeb at-Tahdheeb (2/7-8). 

Secondly: 

A meaning similar to that of the hadeeth quoted above was narrated in the words of some of the Sahaabah (may Allah be pleased with them). There follows a discussion on the strength of the reports that were narrated: 

~1~

Al-Bukhaari narrated in his Saheeh (6194) via Ismaa‘eel ibn Abi Khaalid, who said: I said to Ibn Abi Awfa: Did you see Ibraaheem, the son of the Prophet (blessings and peace of Allah be upon him)? He said: He died in infancy; if it had been decreed that there should be any Prophet after Muhammad (blessings and peace of Allah be upon him), his son would have lived, but there is no Prophet after him. 

~2~

It was narrated that Ismaa‘eel ibn ‘Abd ar-Rahmaan as-Suddi said: I heard Anas ibn Maalik (may Allah be pleased with him) say: If Ibraaheem, the son of the Prophet (blessings and peace of Allah be upon him), had lived, he would have been a man of truth, a Prophet.

Narrated by Ahmad in al-Musnad (19/359, 21/402, and elsewhere). The commentators on al-Musnad said: Its isnaad is hasan because of as-Suddi. End quote. 

To sum up, the meaning of the hadeeth is sound and is narrated in mawqoof reports from Anas and Ibn Abi Awfa; it is not the words of the Prophet (blessings and peace of Allah be upon him). 

Thirdly: 

The scholars differed concerning these reports that were narrated from the Sahaabah; there are two views: 

The first view: 

Some of the scholars rejected this idea and refuted what may be understood from them of Prophethood being inheritable. 

Ibn ‘Abd al-Barr (may Allah have mercy on him) said, commenting on the words of Ibn Abi Awfa: 

I do not know what this is. Nooh (peace be upon him) fathered sons who did not become Prophets, and those who were not Prophets did father Prophets; hence it is possible that a Prophet may father one who is not a Prophet. And Allah knows best. If a Prophet could only father a Prophet, then everyone would have been a Prophet, because everyone is descended from Nooh (peace be upon him). Adam was a Prophet to whom Allah spoke directly, and I do not know of any Prophet among those who were born from his loins except Sheeth (Seth).

End quote from al-Istee‘aab (1/60). 

Imam an-Nawawi (may Allah have mercy on him) said: 

With regard to what is narrated from some of the earlier generations, “If Ibraaheem had lived he would have been a Prophet,” it is false and is speaking of unseen matters in an outrageous and audacious manner, rushing headlong into error. And Allah is the One Whose help we seek.

End quote from Tahdheeb al-Asma’ wa’l-Lughaat (1/103).

The second view: 

Some other scholars accepted the reports mentioned above, but they said that the conditional clause in them is not binding and does not indicate that that could happen. 

Al-Haafiz ibn Hajar (may Allah have mercy on him) said, commenting on the words of Ibn Abi Awfa (may Allah be pleased with him):

Such a thing cannot be said on the basis of personal opinion. There were many scholars who narrated that – he mentioned the hadeeth of Ibn ‘Abbaas and the hadeeth of Anas, both of which are quoted above, then he said: There are a number of saheeh hadeeths from these Sahaabah, saying that they stated that. I do not know what made an-Nawawi object to that so emphatically. It may be that the reports from the Sahaabah mentioned above did not reach him, and what did reach him was from people other than the Sahaabah, who came after them, and that is why he said that. 

Before him, this idea was rejected by Ibn ‘Abd al-Barr, even though those who narrated the reports from the Sahaabah mentioned it with the conditional phrase.

End quote from Fath al-Baari (10/578). 

Mullah ‘Ali al-Qaari (may Allah have mercy on him) said:

It is not necessarily the case that what is mentioned in the conditional clause could have happened, so this does not contradict the fact that he (blessings and peace of Allah be upon him) was the Seal of the Prophets. That is similar to what he (blessings and peace of Allah be upon him) said according to the marfoo‘ report narrated by Ahmad, at-Tirmidhi and al-Haakim, from ‘Uqbah ibn ‘Aamir: “If there were to be any Prophet after me, it would be ‘Umar ibn al-Khattaab.” Allah, may He be glorified, knows best what happened, what is happening, and what will not happen, and if it is to happen, He knows best how it will happen.

End quote from Mirqaat al-Mafaateeh Sharh Mishkaat al-Masaabeeh (9/3721 and 9/3932). See also an important footnote in al-Asraar al-Marfoo‘ah fi’l-Akhbaar al-Mawdoo‘ah (p. 290); and al-Haawi by as-Suyooti (2/119). 

Fourthly: 

In fact we are astounded by the use of this hadeeth – assuming that it is saheeh – to support the argument that it is possible for someone to have been a prophet after the death of the Prophet (blessings and peace of Allah be upon him). The context of the hadeeth points to the exact opposite of that. It seems that what is intended by this hadeeth is to announce the end of Prophethood with the death of the Prophet (blessings and peace of Allah be upon him), and that that status will never be attained by any human after him; if that were possible, the most deserving of it would be Ibraaheem, the son of the Prophet (blessings and peace of Allah be upon him). But Allah, may He be glorified and exalted, caused him to die for great reasons known to Him only, so he was not a prophet and no one else will ever be a prophet either. What clearer explanation can there be for one who seeks guidance? But the whims and desires of the heart and its blindness to the truth cause people to distort the words and misinterpret the text. Allah, may He be glorified and exalted, says (interpretation of the meaning): “So because of their breach of their covenant, We cursed them, and made their hearts grow hard. They change the words from their (right) places…” [al-Maa’idah 5:13]. 

Fifthly: 

It is well known to the linguists that the word law (if) does not indicate the possibility of a thing happening. The grammarians say that it is a word used to indicate that a thing cannot happen because another thing cannot happen. This occurs frequently in the Qur’an, as in the verses (interpretation of the meaning): “Say (O Muhammad SAW to these polytheists, pagans, etc.): ‘If there had been other aliha (gods) along with Him as they assert, then they would certainly have sought out a way to the Lord of the Throne (seeking His Pleasures and to be near to Him)’” [al-Isra’ 17:42] and “Had there been therein (in the heavens and the earth) gods besides Allah, then verily both would have been ruined” [al-Anbiya’ 21:22]. Would any wise person say that these verses indicate that it is possible for there be to other gods besides Allah? 

Similarly, the context of the hadeeth clearly indicates that what is meant here is hypothetical. A hypothesis does not mean that something could happen; rather it may indicate that a thing is impossible according to the shar‘i text, but it is mentioned in order to convey an idea. 

Sixthly: 

By quoting the reports of the Sahaabah we find proof of the opposite of their argument. That is to be found in the words of Ibn Abi Awfa, quoted above from the report of al-Bukhaari: “but there is no Prophet after him”. This is a clear statement that no one who comes after the Prophet (blessings and peace of Allah be upon him) will be a Prophet. 

Shaykh al-Albaani (may Allah have mercy on him) said: 

Once this is understood, it will be clear to you that the Qadianis are mistaken in quoting the phrase, “If Ibraaheem had lived, he would have been a Prophet”, to support their false claim that Prophethood continued after the death of the Prophet (blessings and peace of Allah be upon him), because this hadeeth is not proven to be soundly narrated from him (blessings and peace of Allah be upon him). If they try to strengthen their argument by quoting the reports mentioned above, as we have done, that will refute their argument, as they indicate the opposite. These reports clearly state that the reason why Ibraaheem died in infancy was that there was to be no Prophet after him (blessings and peace of Allah be upon him). Perhaps they may argue about that – as they always do – and try to undermine the proof indicated by the reports by saying that they are not narrated from the Prophet (blessings and peace of Allah be upon him); but they can never escape what we have proven beyond any doubt, which is that their evidence is weak, even with regard to the first report, because it was never attributed soundly to the Prophet (blessings and peace of Allah be upon him).

End quote from as-Silsilah ad-Da‘eefah (1/388). 

Finally: 

With regard to the Qadiani sect (also known as the Ahmadis), contemporary scholars are unanimously agreed that they are outside the pale of Islam, because their beliefs include things that constitute kufr and are contrary to the fundamental teachings of Islam. There have been dozens of fatwas and statements from fiqh councils, among the most significant of which is the statement of the Islamic Fiqh Council belonging to the Organization of the Islamic Conference (no. 4 (4/3)). This sect has gone against the definitive consensus of the Muslims that there is no Prophet after our Prophet Muhammad (blessings and peace of Allah be upon him); this is indicated by a number of texts of the Qur’an and saheeh Sunnah. See the answer to question no. 113393 

On our website there are several answers which discuss them in detail; please see answers no. 4060 and 144765 

And Allah knows best.