What lesson did the Prophet Muhammad (saw) teach when he spoke kindly to someone who he initially judged?
      Narrated '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)."