Jami` at-Tirmidhi 587
جامع الترمذي#587SahihIbn Abbas narrated:"The Messenger of Allah would glance toward the right and the left during Salat but he would not turn his neck to look behind him
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
Zubair Ali ZaiIsnaad Hasan
In-book reference: 6:44