Sunan Ibn Majah 870
سنن ابن ماجه#870SahihIt was narrated that Abu Mas’ud said:“The Messenger of Allah (ﷺ) said: ‘No prayer is acceptable in which a man does not settle his spine when bowing and when prostrating.’”
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih
In-book reference: 5:68