Musannaf Ibn Abi Shaybah

Hazrat Shaddad bin Aus narrates that the Messenger of Allah, peace and blessings be upon him, said to him: Shall I not guide you to the chief supplication for seeking forgiveness (Sayyidul Istighfar)? You should say these words: O Allah! You are my Lord. There is no deity except You. You created me and I am Your servant. And I strive to fulfill Your promise and covenant as much as I am able. I seek refuge in You from the evil of what I have done, and I acknowledge Your blessings upon me, and I confess my sins before You, so forgive me. For surely, none forgives sins except You. There is no servant who says these words during the day, and then dies before evening comes, or says them in the evening and then dies before morning comes, except that he will be among the people of Paradise.