"When any one of you leads the people in prayer, let him make it short, for among them are the sick, the weak and the elderly. And when any one of you prays by himself, let him make it as long as he wishes."  

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا صَلَّى أَحَدُكُمْ بِالنَّاسِ فَلْيُخَفِّفْ فَإِنَّ فِيهِمُ السَّقِيمَ وَالضَّعِيفَ وَالْكَبِيرَ فَإِذَا صَلَّى أَحَدُكُمْ لِنَفْسِهِ فَلْيُطَوِّلْ مَا شَاءَ  

It was narrated from Anas that the Prophet ﷺ used to make his prayer very brief but still complete when leading people.  

أَنَّ النَّبِيَّ ﷺ كَانَ أَخَفَّ النَّاسِ صَلاَةً فِي تَمَامٍ  

"I stand in prayer, then I hear a child crying, so I make my prayer brief, because I do not want to cause hardship for his mother."  

عَنِ النَّبِيِّ ﷺ قَالَ إِنِّي لأَقُومُ فِي الصَّلاَةِ فَأَسْمَعُ بُكَاءَ الصَّبِيِّ فَأُوجِزُ فِي صَلاَتِي كَرَاهِيَةَ أَنْ أَشُقَّ عَلَى أُمِّهِ