Praise be to Allah

Firstly: 

Ibn Abi Shaybah (may Allah have mercy on him) narrated in his Musannaf (29256) with a saheeh isnaad from Ibn ‘Umar that he said: Whoever says following every prayer and when he goes to bed, ‘Allahu akbar kabeera ‘adad ash-shaf‘i wa’l-witr, wa kalimaat Allah at-taammaati at-tayyibaati al-mubaarakaat (Allah is Most Great the number of the even and the odd, and the blessed, pure, perfect words of Allah)’ three times, and ‘Laa ilaaha ill-Allah (there is no god but Allah) the same number of times, they will be light  for him in his grave, and light on the jisr (bridge), and light on the siraat (bridge over Hell), until they admit him to Paradise, or until he enters Paradise.

See question no. 228406

What is meant by following every prayer is every obligatory prayer, because that is what is meant when prayer is mentioned in general terms. That is stated in more than one hadith that was narrated about the adhkaar to be recited following the prayers.

Al-Bukhaari (844) narrated from al-Mugheerah ibn Shu‘bah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) used to say, following every obligatory prayer: “Laa ilaaha ill-Allah wahdahu laa shareeka lah, lahu’l-mulk wa lahu’l-hamd wa huwa ‘ala kulli shay’in qadeer, Allaahumma laa maani’ lima a’tayta wa laa mu’ti lima mana’ta wa la yanfa’ dhaa’l-jadd minka al-jadd (There is no god except Allah alone with no partner or associate, His is the sovereignty and to Him be praise and He is able to do all things. O Allah, none can withhold what You give and none can give what You withhold, and no wealth or majesty can benefit anyone for from You is all wealth and majesty).”

And Muslim (596) narrated from Ka‘b ibn ‘Ujrah that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Dhikrs after the prayer, the one who says them or does them after each obligatory prayer will not be disappointed: thirty-three tasbeehahs, thirty-three tahmeedahs and thirty-four takbeerahs.”

Al-Haafiz (may Allah have mercy on him) said in his commentary on the first hadith:

The apparent meaning of the words “every prayer” includes both obligatory and voluntary prayers, but most of the scholars interpreted it as referring to the obligatory prayers. In the hadith of Ka‘b ibn ‘Ujrah that was narrated by Muslim it specifies that what is meant is the obligatory prayers. It is as if they interpreted general references to prayer as referring to them (the obligatory prayer). End quote.

Fath al-Baari (2/328)

Ahmad (6498) narrated that ‘Abdullah ibn ‘Amr ibn al-‘Aas said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “There are two qualities, whoever adheres to them they will admit him to Paradise. They are simple but those who do them are few.” They said: What are they, O Messenger of Allah? He said: “To praise Allah, magnify Him and glorify Him following every obligatory prayer, ten times each; and when you go to bed, glorify Allah and magnify Him and praise Him one hundred times each. (That will be) two hundred and fifty on the tongue and two thousand five hundred in the Balance.

It was classed as hasan by the commentators on al-Musnad. 

The words in this hadith, “following every obligatory prayer … and when you go to bed” are like the words in the hadith of Ibn ‘Umar, “Whoever says following every prayer and when he goes to bed”. 

What is referred to in both cases is the obligatory prayers. 

The words “and when he goes to bed” refer to the adhkaar of going to sleep. The scholars differed concerning the adhkaar of going to sleep: are they to be said when going to sleep at night only, or can they be said when going to sleep during the day too? 

This has been discussed in fatwa no. 221734 

What is meant by the words “‘Laa ilaaha ill-Allah (there is no god but Allah)’ the same number of times” is saying “Laa ilaaha ill-Allah ‘adad ash-shaf ‘i wa’l-witr, wa kalimaat Allah at-taammati at-tayyibaati al-mubaarakaat (There is no god but Allah, the number of the even and the odd, and the blessed, pure, perfect words of Allah)’” three times, as one did with the phrase beginning with takbeer (‘Allahu akbar’). 

What is meant by the even and the odd is all of creation, some of which is even and some is odd.

 Al-Qaasimi (may Allah have mercy on him) said:

 The even and the odd means the creation and the Creator. The even refers to all of creation, because of the pairs that are in it, as in the verse in which Allah, may He be exalted, says (interpretation of the meaning): “And of everything We have created pairs, that you may remember (the Grace of Allah)” [adh-Dhaariyaat 51:49]. Mujaahid said: Everything that Allah has created is even numbered (in pairs): heaven and earth, land and sea.

 Jinn and man, sun and moon, disbelief and faith, happiness and misery, guidance and misguidance, night and day.

 The odd numbered (Witr) is Allah, may He be exalted, because it is one of His names, and conveys the same meaning as His names al-Waahid, al-Ahad (the One). Thus Allah swore by His Essence and His creation. [“And by the even and the odd” [al-Fajr 89:3]].

And it was said that what is meant by the even and the odd is everything that exists of essences and concepts, because they can only be either even or odd.

End quote from Mahaasin at-Ta’weel (9/456)

See also: at-Tibyaan fi Aqsaam al-Qur’an by Ibn al-Qayyim (21).

What is meant by the blessed, perfect words of Allah is His decrees, both religious and universal (divine will and decree).

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:

The perfect words of Allah are those that include both justice and truth, as in the verse in which Allah, may He be exalted, says (interpretation of the meaning): “The Word of your Lord is perfect in truth and justice” [al-An‘aam 6:115].

Words here may be understood as referring to universal divine decrees and religious decrees. A person may seek refuge in the religious decrees and words of Allah, such as by reciting Qur’an, for example, such as seeking refuge by reciting Soorat al-Falaq and Soorat an-Naas, or he may seek refuge in the universal decrees, which means that Allah, may He be glorified and exalted, protects him by means of His universal decrees from the accursed Shaytaan. End quote.

Liqa’ al-Baab al-Maftooh (8/14)

With regard to the words “light on the jisr (bridge)”, the well-known view is that the jisr is the siraat, as in the hadith which was narrated by Muslim (183): “…Then the bridge will be set up over Hell, and intercession will be permitted.”

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

The jisr is the siraat. End quote.

Sharh an-Nawawi ‘ala Muslim (3/29)

Al-Bukhaari (may Allah have mercy on him) said in his Saheeh (8/117); 

Chapter: The siraat is the bridge over Hell. End quote.

But the words in the hadith of Ibn ‘Umar, “light over the siraat” rule out the interpretation of the jisr as referring to the siraat, otherwise it would be repetition.

What appears to be the case – and Allah knows best – is that what is meant by the jisr here is the bridge between Paradise and Hell, as the believers will settle the scores that arose among them in this world, as al-Bukhaari (2440) narrated from Abu Sa‘eed al-Khudri (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “When the believers have been saved from the Fire, they will be detained at a bridge between Paradise and Hell, and they will settle the scores that arose among them in this world until, when they have been purified and cleansed, permission will be given to them to enter Paradise.”

With regard to the light on the siraat, it is the light that will be given to the believer and withheld from the hypocrite. Allah, may He be exalted, says (interpretation of the meaning):

“the Day that Allah will not disgrace the Prophet (Muhammad (blessings and peace of Allah be upon him)) and those who believe with him, their Light will run forward before them and with (their Records Books of deeds) in their right hands they will say: ‘Our Lord! Keep perfect our Light for us (and do not put it off till we cross over the Sirat (a slippery bridge over the Hell) safely) and grant us forgiveness. Verily, You are Able to do all things’”

[at-Tahreem 66:8]

“On the Day when the hypocrites men and women will say to the believers: ‘Wait for us! Let us get something from your light!’ It will be said: ‘Go back to your rear! Then seek a light!’ So a wall will be put up between them, with a gate therein. Inside it will be mercy, and outside it will be torment”

[al-Hadeed 57:13].

And Allah knows best.