Sahih al-Bukhari 700
Sahih al-Bukhari · Book 10: Call to Prayers (Adhaan) · If the Imam prolongs the Salat (prayer) and somebody has an urgent work or need and so he leaves the congregation and offers Salat alone.
Narrated Mu`adh bin Jabal:
حَدَّثَنَا مُسْلِمٌ ، قَالَ حَدَّثَنَا شُعْبَةُ ، عَنْ عَمْرٍو ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ ، أَنَّ مُعَاذَ بْنَ جَبَلٍ، كَانَ يُصَلِّي مَعَ النَّبِيِّ صلى الله عليه وسلم ثُمَّ يَرْجِعُ فَيَؤُمُّ قَوْمَهُ.
I used to pray the `Isha prayer with the Prophet (ﷺ) and then go to lead my people in the prayer.