What does Islam say about domestic violence?
(source: http://www.al-muslim.org/reality/faq2_4.htm)

Islam condemns domestic violence. Once a number of women came to the prophet, on whom be peace, to complain that their husbands had beaten them. The prophet announced that men who beat their wives are not good men. The prophet also said, "Do not beat the female servants of Allah."

Allah knows that life is not always a bowl of cherries. And so He stipulates that a man must be kind to his wife even if he happens to dislike her (Qur'an 4-19). Allah offers a good reason as to why men should not dislike their wives. Allah says that He has placed much good in women (Qur'an 4:19).

In this regard the prophet Muhammad, on whom be peace, said that no believing man should hold a grudge against a believing woman. So what is a husband to do if he dislikes some things about his wife? This is bound to occur, since no human being is perfect. The prophet instructed that men should look for the agreeable traits in their wives rather than focus on their faults. (See Saheeh Muslim, chapter on advice relating to women).

The prophet also advised men that if they wish to benefit from marriage they should accept their wives as they are rather than try to straighten them out and thus end up in divorce.

In the following verse of the Qur'an, Allah warns men that if they retain their wives in marriage it should not be to take advantage of them. The verse reads: "Retain them in kindness or release them in kindness. But do not retain them to their hurt so that you transgress (the limits). If anyone does that he wrongs his own soul. Do not take God's instructions as a jest" (Qur'an 2:231).

Once the prophet, on whom be peace, was asked what are the obligations of husbands toward their wives. He replied: "Feed her when you eat, and provide her clothing when you provide yourself. Neither hit her on the face nor use impolite language when addressing her" (See Mishkat, chapter on the maintenance of women).

The prophet equated perfect belief with good treatment to one's wife when he said: "The most perfect believer is one who is the best in courtesy and amiable manners, and the best among you people is one who is most kind and courteous to his wives" (see Tirmidhi, chapter on the obligations of a man to his wife). Finally, the prophet, the best example of conduct said: "The best among you is the one who treats his family best."

Some of the last words of the prophet delivered during the farewell pilgrimage enjoins that men should hold themselves accountable before Allah concerning the question of how they treat their wives. Therefore his advice to all men, is as follows:

 "You must treat them with all kindness."