Good Manners and Form (Al-Adab)

Bukhari :: Book 8 :: Volume 73 :: Hadith 80

Narrated 'Aisha:

A man asked permission to enter upon Allah's Apostle. The Prophet said, "Admit him. What an evil brother of his people or a son of his people." But when the man entered, the Prophet spoke to him in a very polite manner. (And when that person left) I said, "O Allah's Apostle! You had said what you had said, yet you spoke to him in a very polite manner?" The Prophet said, "O 'Aisha! The worst people are those whom the people desert or leave in order to save themselves from their dirty language or from their transgression."