Musannaf Ibn Abi Shayba 3:586

Abdah ibn Sulayman narrated to us, from Muhammad ibn Amr, from Abu Salamah, from Abu Hurayrah, who said: A man may pray for sixty years, yet not a single prayer of his is accepted. Perhaps he completes the bowing (ruku') but does not complete the prostration (sujud). Or he completes the prostration but does not complete the bowing.