Sayyiduna Abu Mas’ud (may Allah be pleased with him) reports that the Messenger of Allah (peace and blessings be upon him) said: “The prayer of a person or a man is not sufficient who does not straighten his back equally in bowing (ruku’) and prostration (sujud).” The Imam narrates this in a similar manner from his teacher, Bishr bin Khalid ‘Askari, with the same chain. He has stated these words: “(Who) does not straighten his back in bowing and prostration.”