Good Manners and Form (Al-Adab)
Bukhari :: Book 8 :: Volume 73 :: Hadith 152
A man asked permission to see the Prophet. He said, "Let Him come in; What an evil man of the tribe he is! (Or, What an evil brother of the tribe he is)."
But when he entered, the Prophet spoke to him gently in a polite manner. I said to him, "O Allah's Apostle! You have said what you have said, then you spoke to him in a very gentle and polite manner? The Prophet said, "The worse people, in the sight of Allah are those whom the people leave (undisturbed) to save themselves from their dirty language."
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