Musnad Ahmad 457:3

Yazid narrated to us, Ismail ibn Abi Khalid narrated to us, from Qais ibn Abi Hazim, from Abu Mas’ud, who said: A man came to the Messenger of Allah, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, by Allah, I indeed delay in the morning prayer because of so-and-so"—meaning their Imam. He said: I did not see the Messenger of Allah, peace and blessings of Allah be upon him, more angry in any exhortation than he was on that day. He said: "O people, indeed among you are those who drive people away. So whoever among you leads the people in prayer, let him lighten it, for among them are the weak, the elderly, and those with needs."