Musnad Abu Ya'la al-Mawsili 152:162

Sufyan ibn Waki' narrated to us, my father narrated to us, from Abu Ishaq, from Abu 'Ubaydah, from 'Abdullah, who said: When "When the victory of Allah has come and the conquest" (Surah An-Nasr) was revealed to the Prophet, may Allah bless him and grant him peace, he would frequently say when he recited it and bowed: "Exalted are You, O Allah, our Lord, and by Your praise. O Allah, forgive me; indeed, You are the Accepting of repentance, the Merciful," three times.