Riyad Us-Saliheen (Gardens of the Righteous)

Chapter 246
Supplication at the time of going to Bed and Waking up

1446. Hudhaifah and Abu Dharr (May Allah be pleased with him) reported: Whenever the Messenger of Allah (PBUH) went to bed, he would supplicate: "Bismika-Allahumma amut wa ahya (With Your Name, O Allah, I die and return to life)''; and when he woke up, he would supplicate thus: "Al-hamdu lillahilladhi ahyana ba`da ma amatana, wa ilaihin-nushur (All praise belongs to Allah Who has restored us back to life after causing us to die; and to Him shall we return).''
[Al-Bukhari].

Commentary: The greatest benefit of such Du`a is that one always remembers Allah and keeps Him all the time in mind.