بِاسْمِكَ رَبِّي وَضَعْتُ جَنْبِيْ فَاغْفِرْ لِي ذَنْبِيْ

Bismika Rabbi Wada`tu janbi, faghfir lee janbi

O my Lord, I have slept in your name. You forgive my sins. Abdullah Ibn Amr (RA) said that the Prophet (ﷺ) used to say the above dua when he was lying in bed to sleep.

Reference: Hasan (Shuaib al-Arnait). Musnad Ahmad: 6620