Musnad Ahmad 457:15

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Isma'il, that he heard Qays ibn Abi Hazim narrating from Abu Mas'ud, that a man came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, indeed so-and-so prolongs the prayer for us, until I lag behind." The Messenger of Allah, peace and blessings of Allah be upon him, became angry with an anger I had not seen him display in an exhortation. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, among you are those who drive people away. So whoever leads a people in prayer, let him lighten the prayer for them, for behind him are the elderly, the sick, and those with needs."