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.
باب إِذَا طَوَّلَ الإِمَامُ وَكَانَ لِلرَّجُلِ حَاجَةٌ فَخَرَجَ فَصَلَّى
Sahih al-Bukhari, Book of Call to Prayers (Adhaan)(view book)
Narrated Mu'adh bin Jabal:
I used to pray the 'Isha prayer with the Prophet and then go to lead my people in the prayer.
حَدَّثَنَا مُسْلِمٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ، أَنَّ مُعَاذَ بْنَ جَبَلٍ، كَانَ يُصَلِّي مَعَ النَّبِيِّ ﷺ ثُمَّ يَرْجِعُ فَيَؤُمُّ قَوْمَهُ.
Classification
Narrated 'Amr:
Jabir bin 'Abdullah said, "Mu'adh bin Jabal used to pray with the Prophet and then go to lead his people in prayer Once he led the 'Isha' prayer and recited Surat "Al-Baqra." Somebody left the prayer and Mu'adh criticized him. The news reached the Prophet and he said to Mu'adh, 'You are putting the people to trial,' and repeated it thrice (or said something similar) and ordered him to recite two medium Suras of Mufassal." ('Amr said that he had forgotten the names of those Suras).
وَحَدَّثَنِي مُحَمَّدُ بْنُ بَشَّارٍ، قَالَ حَدَّثَنَا غُنْدَرٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرٍو، قَالَ سَمِعْتُ جَابِرَ بْنَ عَبْدِ اللَّهِ، قَالَ كَانَ مُعَاذُ بْنُ جَبَلٍ يُصَلِّي مَعَ النَّبِيِّ ﷺ ثُمَّ يَرْجِعُ فَيَؤُمُّ قَوْمَهُ، فَصَلَّى الْعِشَاءَ فَقَرَأَ بِالْبَقَرَةِ، فَانْصَرَفَ الرَّجُلُ، فَكَأَنَّ مُعَاذًا تَنَاوَلَ مِنْهُ، فَبَلَغَ النَّبِيَّ ﷺ فَقَالَ " فَتَّانٌ فَتَّانٌ فَتَّانٌ " ثَلاَثَ مِرَارٍ أَوْ قَالَ " فَاتِنًا فَاتِنًا فَاتِنٌ " وَأَمَرَهُ بِسُورَتَيْنِ مِنْ أَوْسَطِ الْمُفَصَّلِ. قَالَ عَمْرٌو لاَ أَحْفَظُهُمَا.