Musannaf Ibn Abi Shayba 3:185

Abu Bakr narrated to us, he said: Ibn Mubarak narrated to us, from Muhammad ibn Muslim, from Ibrahim ibn Maysarah, he said: It reached me that Umar used to say in the bowing (ruku) and the prostration (sujud) the measure of five glorifications: "Subhan Allah wa bihamdihi" (Glory be to Allah and by His praise).