The Book of Mosques and Places of Prayer
Ṣaḥīḥ Muslim 649i
Say this
اللَّهُمَّ اغْفِرْ لَهُ اللَّهُمَّ ارْحَمْهُ . حَتَّى يَنْصَرِفَ أَوْ يُحْدِثَ
Allāhumma āghfir lah Allāhumma ārḥamhu . ḥattā yanṣarifa aw yuḥditha
Transliteration generated from the Arabic vowel marks
The full narration
Abu Huraira reported Allah's Messenger (ﷺ) as saying:The servant is constantly in prayer so long as he is in a place of worship waiting for the prayer (to be observed in congregation), and the angels invoke (blessings upon him in these words): O Allah! pardon him. O Allah! show mercy to him, (and they continue to do so) till he returns (from the mosque having completed the prayer) or his ablution breaks. I said: How is the ablution broken? He said: By breaking of the wind noiselessly or with noise
Source
Ṣaḥīḥ Muslim · 649i
- Recorded in Ṣaḥīḥ Muslim, whose narrations are accepted as authentic
Also narrated in Sunan Abī Dāwūd 471.