The Prophet Muhammad (peace be upon him) said the best supplication for forgiveness from God is: “O God, You are my Lord. There is no god but You. You created me and I am Your servant and I try my best to keep my covenant (of faith) with You and to live in the hope of Your promise. I seek refuge in You from (any) evil done by me. I acknowledge Your favors upon me and I acknowledge my sins. So forgive me, for none forgives sins but You.”
The Prophet added: "If somebody recites this during the day with firm faith in it and dies on the same day before the evening, that person will be one of the people of Paradise. And if somebody recites it at night with firm faith in it and dies before the morning, that person will (also) be one of the people of Paradise."
Fiqh-us-Sunnah, Volume 4, Number 115
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