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).
Hadith Referenceالفتح الربانی / أبواب صفة الصلاة / 1701
Hadith Gradingمحدثین:صحیح
Hadith Takhrij«حديث حسن، ويشھد لھذا الحديث ما في قصة المسيء صلاته: ((ثم اركع حتي تطمئن راكعا، ثم ارفع حتي تعتدل قائما، ثُمَّ اسْجُدْ حتي تطمئن ساجدا)) رواه البخاري ومسلم ، (انظر مسند أحمد ترقيم الرسالة: 10799 ترقیم بيت الأفكار الدولية: 10812»
Brief Explanation
Benefits: … Allah Ta'ala not looking towards his prayer means that his prayer is not looked upon with an eye of acceptance; rather, his prayer is declared invalid and rejected, and it is returned back upon him.