Musnad Ahmad 1153:54

'Amr ibn al-Haytham narrated to us, he said: Hisham narrated to us, from Qatadah, from Mutarrif, 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."