Musnad Ahmad 1153:214

Yahya narrated to us, from Sufyan, who said: Mansur narrated to me, from Abu al-Duha, from Masruq, from Aisha, that the Prophet, peace and blessings of Allah be upon him, used to frequently say in his bowing (ruku'): "Glory be to You, O Allah, our Lord, and with Your praise. O Lord, forgive me," interpreting the Quran.