Congregational Prayer and Its Virtue
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 57
وَ إِنَّ اَلنَّبِيَّ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ كَانَ ذَاتَ يَوْمٍ يَؤُمُّ أَصْحَابَهُ فَيَسْمَعُ بُكَاءَ اَلصَّبِيِّ فَيُخَفِّفُ اَلصَّلاَةَ.
The Prophet صلى الله عليه وعلى آله وسلم was leading his companions in prayer one day when he heard the crying of a child, so he shortened the prayer.
- Ṣaḥīḥ al-Faqīh, p. 55