Musnad Ahmad 26:805

Abu Qatan narrated to us, Mas'udi narrated to us, from Abu Ishaq, from Abu 'Ubaydah, from Abdullah ibn Mas'ud, who said: When "When the victory of Allah has come and the conquest" [An-Nasr: 1] was revealed, the Messenger of Allah (peace and blessings of Allah be upon him) would frequently say: "Glory be to You, O Allah, and with Your praise. O Allah, forgive me, for You are the Accepting of repentance. O Allah, forgive me. Glory be to You, O Allah, and with Your praise. O Allah, forgive me. Glory be to You, O Allah, and with Your praise."