السلام عليكم و رحمة الله و بركاتهWhat is the reason for revealation of ayah 40 of al-Baqarah? What is the story?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu`alayhi wa sallam, is His slave and messenger.

In his Al-ʿUjaab Fee Bayaan al-Asbaab, Ibn Hajar recorded the cause of the revelation of this verse, saying “As for the Saying of Allah, the Exalted, {O Children of Israel, remember My favor which I have bestowed upon you and fulfill My covenant [upon you] that I will fulfill your covenant [from Me] …} [Quran, 2:40] Ibn Al-Kalbi said, 'Allah’s, the Almighty, Covenant to the children of Israel is that 'I would send a Prophet from the progeny of Ismaaʿeel .' Muhammad ibn Is'haaq, may Allaah have mercy reported that Ibn ʿAbbaas  said concerning the Saying of Allah, the Exalted, '… and fulfill My covenant …', it means the covenant that they should follow ProphetMuhammad,   and believe in him when Allah sends him as a Messenger. As for the Saying of Allah, {… or conceal the truth while you know [it]} [The Quran, 2:42], the word 'truth' in verse means Prophet Muhammad . This is actually the opinion of Muhammad ibn Thawr and As-Suddi as recorded by At-Tabari.

At-Tabari,   reported on the authority of Ar-Rabeeʿ ibn Anas from Abu Al-ʿAlyah that the Saying of Allah, the Exalted, '… and fulfill My covenant …' refers to the religion of Islam, meaning that they should follow it while the Saying of Allah, the Exalted, {… I will fulfill your covenant …} [Qruan 2:40] means that He, the Almighty, would reward them with Paradise. This is also the opinion narrated on the authority of ʿAbd Ar-Rahmaan ibn Zayd ibn Aslam who recites the Saying of Allah, the Exalted, {Indeed, Allah has purchased from the believers their lives and their properties [in exchange] for that they will have Paradise.} [Quran, 9:111]

Muqaatil ibn Sulaymaan, on his part, explained the Saying of Allah, the Exalted, {… and fulfill My covenant …} in light of His Saying 'And Allah said, {I am with you. If you establish prayer and give Zakat and believe in My messengers and support them and loan Allah a goodly loan, I will surely remove from you your misdeeds and admit you to gardens beneath which rivers flow. But whoever of you disbelieves after that has certainly strayed from the soundness of the way.} [Quran, 5:12]

However, this is not considered a cause of revelation in the technical sense of the word, which is why neither Al-Waahidi nor As-Suyootti etc. recorded it as the cause of revelation of this verse.

It should also be taken into account that most of the verses of the Glorious Quran were revealed for no cause of revelation; that is to say that we should not search for a cause of revelation for each verse.

On that, Dr. ʿAbdullah Al-Juday' said, "As far as the causes of revelation are concerned, the Quran is divided into two kinds, as follows: First, verses that have no causes of a revelation: This actually constitutes the largest part of the Quran, since verses in the very beginning were revealed on the topics of Sharee'ah, which means that they are not dependent on any cause, such as a particular event or question. That is because the Quran is sent down by the One Who fully knows people’s ethics and instinct nature as well as what benefits them. As such, He, the Exalted, started the revelation with the pillars of the Sharee'ah that are beneficial to people.

Second, verses revealed down in light of a particular incident or question:

This kind of verse is similar to the answers given to questions on contemporary issues. In other words, whenever Muslims experienced any issue, He, the Almighty, sent down the solution to His Prophet.” (See Al-Muqaddimaat Al-Asaasiyah Fee ʿUloom Al-Qur’aan by ʿAbdullah Al-Juday’).

Allah knows best.