Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) asked a man: What do you recite when going to sleep? He replied: I recite: 'Bismika Allahumma wada'tu janbi faghfir li' (O Allah, with Your name, seeking its blessing, I have laid down my side, so forgive me). The Prophet (peace and blessings be upon him) said: May Allah Almighty forgive you.
Al-Tabarani recorded it; its chain contains a narrator, Abd al-Rahman bin Ziyad bin An'um, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 17044