Sahih al-Bukhari Book 10, Hadith 97
A man came and said, "O Allah's Messenger (ﷺ)! By Allah, I keep away from the morning prayer only
because So and so prolongs the prayer when he leads us in it." The narrator said, "I never saw Allah's
Apostle more furious in giving advice than he was at that time. He then said, "Some of you make
people dislike good deeds (the prayer). So whoever among you leads the people in prayer should
shorten it because among them are the weak, the old and the needy."
Jabir bin `Abdullah said, "Mu`adh bin Jabal used to pray with the Prophet (ﷺ) and then go to lead his people in prayer Once he led the `Isha' prayer and recited Surat "Al-Baqara." Somebody left the prayer and Mu`adh criticized him. The news reached the Prophet (ﷺ) 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).
Allah's Messenger (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. "