We went out to the Messenger of Allah ﷺ, pledged our allegiance to him, and prayed behind him. From the corner of his eye, he noticed a man who was not keeping his back straight during the bowing and prostration. When the Prophet ﷺ finished the prayer, he said, "Company of Muslims, there is no prayer for the one who does not keep his back straight during the bowing and prostration."
خرجنا إلى رسول الله ﷺ فبايعناه وصلينا خلفه، فلمح بمؤخر عينه رجلا لا يقيم صلاته- يعني صلبه في الركوع والسجود، فلما قضى النبي ﷺ، قال: يا معشر المسلمين! لا صلاة لمن لا يقيم صلبه في الركوع والسجود.
Ibn Majah (871) reported it from Abu Bakr bin Abu Shayba, who said, Mulazim bin Amr narrated to us, from Abdullah bin Badr, who said, Abdul-Rahman bin Ali bin Shayban informed me, from his father Ali bin Shayban, and he then related the hadith. Its chain of transmission is sahih, and Ibn Khuzayma (593) and Ibn Hibban (1891) also graded it sahih, both reporting it through the route of Mulazim bin Amr with the same wording. Busiri said in Zawaid Ibn Majah, "Its chain of transmission is sahih and its narrators are trustworthy."