Musnad Ahmad 28:481

Rawh narrated to us, Hatim ibn Abi Saghirah narrated to us, Abu Balj narrated to us, from ‘Amr ibn Maymun, from ‘Abdullah ibn ‘Amr, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Whoever says: 'There is no god but Allah, and Allah is the Greatest, and praise be to Allah, and glory be to Allah, and there is no power and no strength except by Allah,' his sins shall be expiated, even if they were like the foam of the sea."