From Sahih Muslim (Hadith 1508):
Abu Huraira reported Allah's Messenger (ﷺ) as saying:The angels invoke blessings on everyone among you so long as he is in a place of worship with these words: O Allah! pardon him, O Allah, have mercy upon him, (and they continue to do so) as long as, he ablution (of the worshipper) is not broken, and one among you is in prayer and so long as he is detained for the prayer
Reference: Muslim 1508