The Prophet (ﷺ) said "The most superior way of asking for forgiveness from Allah is: O Allah, You are my Lord, there is none worthy of worship except You. You have created me, and I am Your servant, and I am faithful to Your covenant and promise as much as I can. I seek refuge in You from the evil of what I have done. I acknowledge Your blessings upon me, and I admit my sins. So forgive me, for none forgives sins except You.
(Allahumma anta Rabbi la ilaha illa anta, Khalaqtani wa ana `Abduka, wa ana `ala `ahdika wa wa`dika mastata`tu, A`udhu bika min Sharri ma sana`tu, abu'u Laka bini`matika `alaiya, wa abu'u laka bidhanbi faghfir lee fa innahu la yaghfiru adhdhunuba illa anta)
The Prophet (ﷺ) added. "If somebody recites it during the day with firm faith in it, and dies on the same day before the evening, he will be from the people of Paradise; and if somebody recites it at night with firm faith in it, and dies before the morning, he will be from the people of Paradise."