Musnad Ahmad 30:1598

Makki ibn Ibrahim narrated to us, Abdullah—meaning Ibn Sa'id—narrated to us, from Sumayy, from Abu Salih, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever says: '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'—whoever says it ten times when he enters the morning, one hundred good deeds shall be written for him by it, one hundred evil deeds shall be erased from him by it, it shall be for him the equivalent of freeing a slave, and he shall be protected by it on that day until he enters the evening. And whoever says the like of that when he enters the evening, he shall have the like of that."