Silsilat al-Ahadith al-Sahihah

Abu Hurairah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "A man may perform prayer for sixty years, but none of his prayers are accepted. Perhaps this is because he completes the bowing (ruku') but does not complete the prostration (sujud), or he completes the prostration but does not complete the bowing."