📖 Shaddad bin Aus RadhiAllahu 'anhu narrated: Allah's noble Messenger Muhammad SallAllahu 'alaihi wa sallam said, "The best supplication for seeking forgiveness ('Sayyid-ul- Istighfaar') is to say: 'Allahumma Anta Rabbi, laa ilaaha illaa Anta, khalaqtani wa ana 'abduka, wa ana 'alaa 'ahdika wa wa'duka mastata't, a'udhu Bika min sharri maa sana't, abu'u Laka bini'matika 'alayy, wa abu'u bidhanbi faghfir lee, fa innahu la yaghfirudh-dhunooba illaa Anta. (O Allah! You are my Rabb (Lord, Cherisher and Sustainer). There is no true god except You. You (Allah) have created me, and I am Your slave, and I hold to Your Covenant as far as I can. I seek refuge in You from the evil of what I have done. I acknowledge the favours that You (Allah) have bestowed upon me, and I confess my sins. Pardon me, for none but You (Allah) has the power to pardon).' He who supplicates in these terms during the day with firm belief in it and dies on the same day (before the evening), he will be one of the dwellers of Paradise; and if anyone supplicates in these terms during the night with firm belief in it and dies before the morning, he will be one of the dwellers of Paradise."
[Sahih Al-Bukhari]
Reference: Riyad As-Salihin 1875
In-book reference: Book 19, Hadith 7