It is narrated from Sayyiduna Shaddad bin Aws (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The master supplication for forgiveness (Sayyid al-Istighfar) is that the servant says: '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 bidhunubi, wa abu'u laka bini'matika alayya, faghfir li, innahu la yaghfiru al-dhunuba illa anta' (O Allah, You are my Lord, there is no god but You. You created me and I am Your servant, and I abide by Your covenant and Your promise as much as I am able. I seek refuge with You from the evil of what I have done. I acknowledge before You my sins, and I acknowledge Your favours upon me, so forgive me, for none forgives sins except You)." This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.