Sahih Al-Bukhari, Vol.8, Hadith No. 318

Narrated Shaddad bin Aus:
The Prophet (S.A.W) said, "The most superior way of asking for forgiveness from Allah is:

* Allahumma Anta Rabbi,
la ilaha illa Anta.
Anta khalaqtani wa ana 'abduka,
wa ana ala 'ahdika wa wa' dika mastata' tu.
A'udhu bika min sharri ma sanatu,
abu'u laka bini' matika 'alaiya,
wa abu 'ulaka bidhanbi faghfirli fa innahu la yaghfiru adhdhunuba illa Anta

The Prophet (S.A.W) added: "If somebody recites them during the day with firm faith in it, then 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."
(Sahih Al-Bukhari, Vol.8, Hadith No. 318).

* O Allah, You are my Lord!
None has the right to be worshipped but You.
You created me and I am Your slave,
and I am faithful to my covenant and my promise (to You) as much as I can.
I seek refuge with You from all the evil I have done.
I acknowledge before You all the blessings You have bestowed upon me,
and I confess to You all my sins.
So I entreat You to forgive my sins, for nobody can forgive sins except You.