Jami` at-Tirmidhi 3397

Abu Sa`eed (ra) narrated that :the Prophet (ﷺ) said: “Whoever says, when he goes to his bed: ‘I seek forgiveness from Allah, [the Magnificent] the One whom there is none worthy of worship except for Him, the Living, the Sustainer, and I repent to Him (Astaghfirullāha [al-`Aẓim] alladhi lā ilāha illā huw, al-Ḥayyul-Qayyūm, wa atūbu ilaihi)’ three times, Allah shall forgive him his sins if they were like the foam of the sea, even if they were the number of leaves of the trees, even if they were the number of sand particles of `Alij, even if they were the number of the days of the world.”