Why do Muslims have baptism?

All religions have some form of initiation rites in which
people are welcomed as members of the community. Often the particular form these rites
take differs depending on the age of the person being initiated, i.e. whether the person
is an infant, child or adult. 

All three of the Abrahamic
religions, Judaism, Christianity, and Islam have some sort of initiation or welcoming
rituals. The form this takes in Christianity is baptism, involving whole or partial
immersion in water, anointing with oil, and some form of liturgy and prayer. In Islam,
as stated above, this initiation takes the form of community prayer and ritual that does
not involve immersion in water, and thus is not a baptism per
se. 

The Jewish version of initiation of a baby into the
religious community involves prayers and other community rituals for babies of both
genders and circumcision for male infants. Again, this is not baptism, but serves a
similar function of welcoming the child into the religious
community.