Jami` at-Tirmidhi 265

جامع الترمذي#265Sahih

Abu Mas'ud Al-Ansari [Al-Badri] narrated that :Allah's Messenger said: "The Salat is not acceptable if a man is not at rest - meaning his back - while bowing and prostrating

Scholarly Authentication

We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:

Ahmad Muhammad ShakirSahih

Al-AlbaniSahih

Bashar Awad MaaroufHasan Sahih

Zubair Ali ZaiSahih

In-book reference: 2:117

All of Jami` at-Tirmidhi