Hadith # 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)."
The greatest benefit of such Du'a is that one always remembers Allah and keeps Him all the time in mind.