Jami` at-Tirmidhi 281
جامع الترمذي#281SahihAl-Bara said:"When we performed Salat behind Allah's Messenger, he would raise his head from bowing, and no man among us would bend his back until Allah's Messenger prostrated, then we prostrated
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 - Agreed Upon
In-book reference: 2:133