Qur’an 4:3—And if you fear that you shall not be able to deal justly with the orphan-girls, then marry (other) women of your choice, two, or three, or four.
Of course, Muhammad was the exception. He was married to at least eleven women at one time. One of the things we learn from early Muslim history is that women usually don't like having to compete for their husbands' affection. Thus, there was a fierce rivalry among Muhammad's wives, and the prophet of Islam showed great favoritism towards certain wives.
Some women, however, just won't stand for such unfair treatment.
SAUDI ARABIA—A Saudi woman cut her husband’s penis off after he decided to have a second wife under Islamic law which allows a man to have four wives at a time, a newspaper reported on Wednesday.
An ambulance rushed the unnamed man to the nearest medical centre in the capital Riyadh before he was flown by helicopter to a specialized hospital for treatment, 'Sharq' Arabic language daily said.
“His wife begged him not to marry again but he did not listen to her….she then severed his penis with a big knife,” it said.
“He was taken to hospital in a serious condition because of heavy bleeding,” it added without making clear if the man’s penis was restored. (Source)