Musnad Ahmad 26:801

'Abdullah ibn al-Walid narrated to us, Sufyan 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" was revealed, the Prophet, peace and blessings of Allah be upon him, would frequently say: "Exalted are You, O Allah, and with Your praise. O Allah, forgive me, for You are the Accepting of repentance."