Praise be to Allah

Firstly:

The best of the Prophets is our Prophet Muhammad (blessings and peace of Allah be upon him). He is the best of the sons of Adam and the dearest of them to Allah.

The best of the Prophets after him is the Close Friend of the Lord of the Worlds, Ibraaheem (peace be upon him).

Some of the scholars narrated that there was consensus on that. Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:

The best of the Prophets after Muhammad (blessings and peace of Allah be upon him is Ibraaheem al-Khaleel, as it is proven in Saheeh Muslim from Anas that the Prophet (blessings and peace of Allah be upon him) “is the best of mankind.”

This was also stated by the scholars, including ar-Rabee‘ ibn Khuthaym, who said: I do not regard any one as superior to our Prophet, and I do not regard anyone as superior to Ibraaheem after our Prophet. End quote.

Majmoo‘ al-Fataawa (4/317)

There is no difference of scholarly opinion that Muhammad (blessings and peace of Allah be upon him) is the best of them, then after him comes Ibraaheem, then Moosa, according to the well-known view. End quote.

Tafseer Ibn Katheer (5/88).

As-Suyooti (may Allah have mercy on him) said:

We believe that the best of all creation is the Beloved of Allah, the Chosen One, Prophet Muhammad (blessings and peace of Allah be upon him); and the Close Friend of Allah, Ibraaheem, comes next to him in status. He is the best of mankind after him. Some scholars narrated that there was consensus on this point. And Moosaa, ‘Eesaa and Nooh come after Ibraaheem , they are superior to the rest of the Prophets. End quote.

Itmaam ad-Diraayah (p. 17)

Allah, may He be exalted, has told us that He took Ibraaheem as a Close Friend (Khaleel), as He says (interpretation of the meaning):

“And Allâh did take Ibrâhim (Abraham) as a Khaleel (an intimate friend)”

[an-Nisa’ 4:125].

This status (i.e. the status of being a close friend) was not confirmed for any human being except our Prophet Muhammad and Ibraaheem (blessings and peace of Allah be upon them), so they are the best of mankind.

Secondly:

With regard to the hadith that you mentioned, it was narrated by at-Tirmidhi (2995), al-Haakim (3151) and at-Tabari (6/498) via Abu’d-Duha from Masrooq from Ibn Mas‘ood who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Verily every Prophet has allies among the Prophets, and my ally is my father and the Close Friend of my Lord, Ibraaheem.” Then he recited the words (interpretation of the meaning): “Verily, among mankind who have the best claim to Ibrâhim (Abraham) are those who followed him, and this Prophet (Muhammad (blessings and peace of Allah be upon him)) and those who have believed (Muslims). And Allâh is the Walî (Protector and Helper) of the believers” [Aal ‘Imraan 3:68].

Ahmad (3800) and at-Tirmidhi also narrated a similar report via Abu Nu‘aym and Wakee‘ from Sufyaan, from his father, from Abu’d-Duha, from ‘Abdullah, from the Prophet (blessings and peace of Allah be upon him), but there is no mention in it of it being from Masrooq. At-Tirmidhi said: This is more saheeh than the hadith of Abu’d-Duha from Masrooq.

Ibn Abi Haatim (may Allah have mercy on him) said:

I asked my father and Abu Zur‘ah about a hadith that was narrated by Abu Ahmad az-Zubayri and Rawh ibn ‘Ubaadah, from Sufyaan ath-Thawri, from his father, from Abu’d-Duha, from Masrooq, from ‘Abdullah, from the Prophet (blessings and peace of Allah be upon him), who said:  “Verily every Prophet has allies among the Prophets, and my ally is my father and the Close Friend of my Lord, Ibraaheem.” Then he recited the words (interpretation of the meaning): “Verily, among mankind who have the best claim to Ibrâhim (Abraham) are those who followed him, and this Prophet (Muhammad (blessings and peace of Allah be upon him)) and those who have believed (Muslims). And Allâh is the Walî (Protector and Helper) of the believers” [Aal ‘Imraan 3:68]. They both said: This is wrong. It was narrated by the well-versed scholars among the companions of ath-Thawri from ath-Thawri, from his father, from Abu’d-Duha, from ‘Abdullah, from the Prophet (blessings and peace of Allah be upon him), without Masrooq. End quote.

‘Ilal al-Hadith (4/613).

The commentators on al-Musnad said: Those who narrated it with an interrupted isnaad are more sound and more numerous than others. Therefore Abu Zur‘ah, Abu Haatim and at-Tirmidhi regarded the report with the interrupted isnaad as being more likely to be sound.

Nevertheless, al-Haakim classed it as saheeh according to the conditions of the two shaykhs [al-Bukhaari and Muslim], and adh-Dhahabi agreed with him. Similarly, al-Albaani classed it as saheeh in Saheeh Abi Dawood.

Shaykh Ahmad Shaakir (may Allah have mercy on him) said in Tahqeeq Musnad Ahmad: Its isnaad is da‘eef, because it is interrupted (munqati‘). Abu’d-Duha Muslim ibn Subayh did not meet Ibn Mas‘ood.

But it was narrated by at-Tirmidhi via Abu Ahmad from ath-Thawri from his father from Abu’d-Duha from Masrooq from Ibn Mas‘ood, so this isnaad is complete.

Then he narrated it via Abu Nu‘aym and via Wakee‘, both from ath-Thawri as mentioned here, omitting Masrooq from the isnaad. At-Tirmidhi thought that the report of the one who narrated it with an interrupted isnaad is more likely to be sound.

Ibn Katheer narrated it in his Tafseer (2/162-163) from the Sunan of Sa‘eed ibn Mansoor: Abu’l-Ahwaas told us, from Sa‘eed ibn Masrooq [who was the father of Sufyaan ath-Thawri], from Abu’d-Duha, from Masrooq, from Ibn Mas‘ood.

This is another report with a complete isnaad which supports the report of Abu Ahmad that was narrated by at-Tirmidhi. The addition of Masrooq’s name, which makes the isnaad complete, is a trustworthy addition, so it is acceptable. Thus the hadith in and of itself is saheeh.

For more information, please see Kitaab at-Tafseer in Sunan Sa‘eed ibn Mansoor (no. 501). With regard to the meaning of the hadith – if it is sound – al-Mubaarakfoori said in Tuhfat al-Ahwadhi:

“Verily every Prophet has allies” that is, loved ones and friends who are closer to him than others

“among the Prophets” that, these allies are also Prophets.

“and my ally is my father” namely Ibraaheem (peace be upon him); this is explained by the words “and the Close Friend of my Lord.”

“Then he recited the words” that is, he quoted them as proof:

“Verily, among mankind who have the best claim to Ibrâhim” that is, they have more right to be close to him

“are those who followed him” that is, at his time

“and this Prophet” namely Muhammad, because he matches him in most of his teachings

“and those who have believed” of his ummah, for they are the ones who can say: We are following his religion, not you.

“And Allâh is the Walî (Protector and Helper) of the believers” that is, their supporter and protector.

If you say that the words “Verily every Prophet has allies” imply that each one of them had numerous allies,

My response is: No, because what it means is that every single Prophet, with no exception, has an ally.

See: Mirqaat al-Mafaateeh (9/3961)

See also the answer to question no. 149310 and 228450

And Allah knows best.