Musannaf Ibn Abi Shayba 21:235

Muhammad ibn Abd Allah al-Asadi narrated to us, from Ali ibn Salih, from Abu Ishaq, from Amr ibn Murrah, from Abd Allah ibn Salamah, from Ali, who said: The Prophet, may Allah bless him and grant him peace, said to me: "Shall I not teach you words that, if you say them, you will be forgiven—even though you are already forgiven? 'There is no god but Allah, the Forbearing, the Generous. There is no god but Allah, the Most High, the Magnificent. Glory be to the Lord of the seven heavens and the Lord of the Magnificent Throne. Praise be to Allah, Lord of the worlds.'"