A man came to Messenger of Allah ﷺ and said, "O Messenger of Allah ﷺ! By Allah, I fail to attend the morning congregational prayer because so-and-so (i.e., Muʿadh bin Jabal) prolongs the prayer when he leads us for it." I had never seen the Prophet ﷺ more furious in giving advice than he was on that day. He then said, "O people! some of you make others dislike (good deeds, i.e. prayers etc). So whoever among you leads the people in prayer, he should shorten it because among them there are the old, the weak and the busy (needy having some jobs to do). (See Hadith No. 90, Vol. 1)  

جَاءَ رَجُلٌ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ إِنِّي وَاللَّهِ لأَتَأَخَّرُ عَنْ صَلاَةِ الْغَدَاةِ مِنْ أَجْلِ فُلاَنٍ مِمَّا يُطِيلُ بِنَا فِيهَا قَالَ فَمَا رَأَيْتُ النَّبِيَّ ﷺ قَطُّ أَشَدَّ غَضَبًا فِي مَوْعِظَةٍ مِنْهُ يَوْمَئِذٍ ثُمَّ قَالَ يَا أَيُّهَا النَّاسُ إِنَّ مِنْكُمْ مُنَفِّرِينَ فَأَيُّكُمْ مَا صَلَّى بِالنَّاسِ فَلْيُوجِزْ فَإِنَّ فِيهِمُ الْكَبِيرَ وَالضَّعِيفَ وَذَا الْحَاجَةِ  

Messenger of Allah ﷺ said, "If anyone of you leads the people in the prayer, he should shorten it for amongst them are the weak, the sick and the old; and if anyone among your prays alone then he may prolong (the prayer) as much as he wishes. "  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِذَا صَلَّى أَحَدُكُمْ لِلنَّاسِ فَلْيُخَفِّفْ فَإِنَّ مِنْهُمُ الضَّعِيفَ وَالسَّقِيمَ وَالْكَبِيرَ وَإِذَا صَلَّى أَحَدُكُمْ لِنَفْسِهِ فَلْيُطَوِّلْ مَا شَاءَ  

The Prophet ﷺ used to pray a short prayer (in congregation) but used to offer it in a perfect manner.  

كَانَ النَّبِيُّ ﷺ يُوجِزُ الصَّلاَةَ وَيُكْمِلُهَا  

I never prayed behind any Imam a prayer lighter and more perfect than that behind the Prophet ﷺ and he used to cut short the prayer whenever he heard the cries of a child lest he should put the child's mother to trial.  

سَمِعْتُ أَنَسَ بْنَ مَالِكٍ يَقُولُ مَا صَلَّيْتُ وَرَاءَ إِمَامٍ قَطُّ أَخَفَّ صَلاَةً وَلاَ أَتَمَّ مِنَ النَّبِيِّ ﷺ وَإِنْ كَانَ لَيَسْمَعُ بُكَاءَ الصَّبِيِّ فَيُخَفِّفُ مَخَافَةَ أَنْ تُفْتَنَ أُمُّهُ  

The Prophet ﷺ said, "When I start the prayer I intend to prolong it, but on hearing the cries of a child, I cut short the prayer because I know that the cries of the child will incite its mother's passions."  

أَنَّ النَّبِيَّ ﷺ قَالَ إِنِّي لأَدْخُلُ فِي الصَّلاَةِ وَأَنَا أُرِيدُ إِطَالَتَهَا فَأَسْمَعُ بُكَاءَ الصَّبِيِّ فَأَتَجَوَّزُ فِي صَلاَتِي مِمَّا أَعْلَمُ مِنْ شِدَّةِ وَجْدِ أُمِّهِ مِنْ بُكَائِهِ