Sahih Bukhari Volume 008, Book 073, Hadith Number 059A.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 73. Good Manners and Form (Al-Adab)
Narated By 'Aisha : A man asked permission to enter upon the Prophet. When the Prophet saw him, he said, "What an evil brother of his tribe! And what an evil son of his tribe!" When that man sat down, the Prophet behaved with him in a nice and polite manner and was completely at ease with him. When that person had left, 'Aisha said (to the Prophet). "O Allah's Apostle! When you saw that man, you said so-and-so about him, then you showed him a kind and polite behavior, and you enjoyed his company?" Allah's Apostle said, "O 'Aisha! Have you ever seen me speaking a bad and dirty language? (Remember that) the worst people in Allah's sight on the Day of Resurrection will be those whom the people leave (undisturbed) to be away from their evil (deeds)."