Musannaf Ibn Abi Shayba 3:190

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, from Abu Ma‘shar, from al-Hasan, that he used to say: The middle [path] regarding the bowing (ruku‘) and the prostration (sujud) is that a man should say in his bowing and his prostration: "Subhan Allah wa bi-hamdihi" (Glory be to Allah and by His praise) three times.