 According to Shia Muslims, the prophet Muhammad sanctioned fixed-term marriage, called "muta'a" in Iraq and "sigheh" in Iran, which according to some Western writers, has allegedly been used as a legitimizing cover for sex workers, in a culture where prostitution is otherwise forbidden.Sunni Muslims, who make up the majority of Muslims worldwide, believe the practice of nikah mut‘ah was revoked and ultimately forbidden by second Sunni caliph, Umar.Shias deem all sexual relations outside of proper marriage (the only being nikah or nikah mutah) as haram.