Musnad Ahmad 1153:2053

Rawh narrated to us, he said: Shu'bah narrated to us, from Qatadah, from Mutarrif ibn 'Abdullah ibn al-Shikhkhir, from 'Aishah, that the Messenger of Allah (peace and blessings of Allah be upon him) used to say in his bowing (ruku') and his prostration (sujud): "Most Glorified, Most Holy, Lord of the angels and the Spirit."