Sahih Muslim Book 6, Hadith 74
" His face would turn towards us."
When we prayed behind the Messenger of Allah (ﷺ) we cherished to be on his right side so that his face would turn towards us (at the end of the prayer), and he (the narrator) said: I heard him say: O my Lord! save me from Thy torment on the Day when Thoil, wouldst raise or gather Thy servants.
When the prayer commences then there is no prayer (valid), but the obligatory prayer. This hadith has been narrated by Warqa' with the same chain of transmitters.