"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."
Jami` at-Tirmidhi Book 6, Hadith 44
← Previous Hadith the Messenger of Allah said: "Whoever prays Fajr in congregation, then sits remembering Allah until the sun has risen, then he prays two Rak'ah, then for him is the reward like that of a Hajj and Umrah." He said: "The Messenger of Allah said: 'Complete, complete, complete.'"

Jami` at-Tirmidhi Book 6, Hadith 43 Next Hadith → "The Prophet would glance during Salat" and he mentioned a similar narration.

Jami` at-Tirmidhi Book 6, Hadith 45