Musnad Ahmad 1363

It was narrated that ‘Ali (رضي الله عنه) said: The Messenger of Allah (رضي الله عنه) said: "Shall I not teach you some words which, if you say them you will be forgiven, even though you are already forgiven: There is no god but Allah, Most High, the Almighty; there is no god but Him, the most Forbearing the Most Generous; glory be to Allah, Lord of the Mighty Throne; praise be to Allah, Lord of the Worlds.”