Sunan an-Nasa'i — The Book of the Masjids — Hadith No: 733
Translation
It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:"The angels send Salah upon any one of you so long as he is in the place where he prays, and so long as he does not invalidate his ablution, (saying): 'O Allah, forgive him, O Allah, have mercy on him