Several ahadith, by different reporters, highlight the fact that the Prophet (peace be upon him) never used foul language. Anas ibn Malik reports: "God's Messenger was not given to the use of foul language, cursing or abusive names. When he expressed displeasure with someone, he would say, 'What is wrong with him; may he have dust on his forehead.'" (Bukhari.) In answer to a question about the Prophet's manners, Aishah said: "He never used foul or obscene language. Nor was he quarrelsome in the market place. He did not repay a bad turn with a similarly bad one, but would rather forgive and forebear." (Ahmad, Tirmidhi)
Some people put on an appearance when they are out and meet others. The Prophet, however, did not put any appearance other than his real manners. For example: "Some of his Companions visited Umm Salamah, his wife. They said to her: "Mother of the believers, tell us what is God's Messenger like in the privacy of his home." She said: "He is always the same in public and in private." (Ahmad, Tabarani.)
These ahadith together give us a picture of a person who turns away from whatever is unbecoming and to whom good conduct comes naturally; he realizes that whatever comes from God is good. He is the first to implement it, at home and in public. The Prophet was the same in public and with his own family: he never used abusive or insulting language, cursed or engaged in a verbal quarrel. He was aware of his task of "bringing good manners to perfection."
"Muhammad: His Character and Conduct" - Adil Salahi