It is narrated from Sayyiduna Abu Malik al-Ash'ari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you wishes to sleep, let him say: I believe in Allah and I reject the taghut (false deities). The promise of Allah is true, and the messengers have spoken the truth. O Allah, I seek refuge in You from the calamities that come by night, except a visitor that comes with good."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3441