1446/1- Hudhayfah and Abu Dharr (may Allah be pleased with them) reported: “When Allah’s Messenger (may Allah’s peace and blessings be upon him) went to bed he would say: Bismika Allāhumma amūtu wa ahya (In Your name, O Allah, I die and return to life), and when he woke up, he would say: Al-hamdu lillāhi alladhi ahyāna ba‘dama amātana wa ilayhi an-nushūr (Praise be to Allah Who restored us back to life after He caused us to die, and unto Him is the resurrection).” [Narrated by Al-Bukhāri]
1) This Dhikr suits the occasion of going to bed because sleep is a minor form of death, so waking up from it reminds the slave of resurrection from the major death. This increases the one’s belief in resurrection, so that he would always have it present in his mind.
2) It is out of Allah’s favor upon His slaves that He legislated for them Dhikr to be said in every occasion of their lives, whereby all their times would be filled with remembrance or Allah.