It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Allah Almighty does not look towards the prayer of the person who does not straighten his back in bowing (ruku) and prostration (sajdah).

Taliq bin Ali Hanafi (may Allah be pleased with him) has also narrated a similar type of hadith from the Noble Prophet (peace and blessings be upon him and his family).

It is narrated from Sayyiduna Ali bin Shiban (may Allah be pleased with him), he says: I came to the Messenger of Allah (peace and blessings be upon him) as part of a delegation. We performed prayer behind the Noble Prophet. The Prophet glanced from the corner of his eye at a man who was not straightening his back in bowing (ruku) and prostration (sujud). When the Prophet (peace and blessings be upon him) finished the prayer, he said: O assembly of Muslims! Indeed, that man has no prayer, who does not straighten his back in bowing and prostration.

It is narrated from Sayyiduna Abu Qatadah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: The worst person in terms of theft is the one who steals from his prayer. The people asked: O Messenger of Allah! How does he steal from his prayer? He (peace and blessings be upon him) said: He does not complete the bowing and prostration, or he said: He does not straighten his back in bowing and prostration.

Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) also narrates a similar hadith from the Noble Prophet (peace and blessings be upon him).

Sayyiduna Anas bin Malik (may Allah be pleased with him) says: When the Messenger of Allah (peace and blessings be upon him) would raise his head from prostration or bowing, he would remain for such a long time that we would say: Has the Messenger of Allah (peace and blessings be upon him) forgotten?