Trustworthy narrators have related from Imam al-Sadiq (AS), who said: 'When Ali (AS) spent the night upon the bed [of the Prophet], God revealed to two of His angels — among the angels there were no two more closely bound in affection and brotherhood than they — and said: I am going to cause one of you to die; choose — which of you will prefer his companion for survival? Each of them pushed death away onto the other, and each preferred survival for himself. Then God revealed to them: Where do you stand beside My servant who is content with death, who has spent the night upon the bed of his cousin, shielding him from destruction with his own life? Truly I know from his inmost heart that the loss of his own life is dearer to him than that a single hair of his cousin's head should be touched. Descend to him and guard him until morning.' Thereupon the angels said: 'Blessings upon you, O son of Abu Talib — you are the beloved, the self-sacrificing consoler.' (al-Risala al-Alawiyya fi Fadl Amir al-Mu'minin, vol. 1, p. 60)
Imam al-Sadiq (AS) said concerning the Laylat al-Mabit: When that event was about to take place, God said to two angels who, among all the angels, had the greatest friendship and brotherhood with one another: I intend to cause one of you two to die! Which of you will prefer the other over himself? Each of the two warded death away from himself and wished survival for himself. God said to the two: Now behold this servant of Mine, Ali, who — to preserve the life of his brother in faith, Muhammad — has consented to embrace death and give himself up to be killed. Thereupon the angels said: O Ali, may the station God has granted you be blessed to you! And God revealed to those two angels that they should descend that night to the room where Ali lay sleeping and watch over Ali until morning.