Musannaf Ibn Abi Shayba 21:187

Abu Mu'awiyah narrated to us, from al-A'mash, from Habib, from 'Abdullah ibn Babah, from Abu Hurayrah, who said: "Whoever says when he goes to his bed: 'There is no god but Allah, alone, with no partner; to Him belongs the dominion, and to Him belongs the praise, and He is capable of all things. Glory be to Allah and by His praise, praise be to Allah, there is no god but Allah, and Allah is the Greatest,' his sins will be forgiven, even if they were like the foam of the sea."