صحیح ابن حبان
Ibn Hibban
كتاب الصلاة
Book of Prayer
باب صفة الصلاة - ذكر الإخبار عن نفي جواز صلاة المرء إذا لم يقم أعضاءه في ركوعه وسجوده
Chapter on the Manner of Prayer – Report indicating that prayer is invalid if the limbs are not straightened in bowing and prostration
2 hadith
Hadith 1892
Sayyiduna Abu Mas’ud (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) said: “That prayer is not valid in which a person does not keep his back straight during bowing (ruku’) and prostration (sujud).”
Hadith 1893
Sayyiduna Abu Mas’ud (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) said: “The prayer of that person is not valid who does not keep his back straight during bowing (ruku’) and prostration (sujud).”