Muslims do not celebrate baptism in the Christian sense. Islam challenges the authority of baptism, citing the Quran's declaration that participation in the religion is itself the baptism of Allah. There are similar rituals, however, including ablution with water prior to prayer and a testimony of faith for newborn children.
The testimony of faith for newborn children in Islam is called the Shahadah. It is similar to baptism in the Christian sense because it serves as the infant's introduction to the faith. Unlike baptism, however, Shahadah does not include the ritual cleansing of original sin with water. Instead, the text of the Shahadah is gently recited into the baby's left and right ears. Voluntary converts to Islam must also declare the Shahadah, preferably in front of a mosque or in the presence of Muslim witnesses.
Whereas Christians use ritual ablution to symbolically wash away sin, Muslims are commanded by the Quran to simply clean themselves with water before praying. They must also ensure that they are similarly cleansed before handling or touching the Quran. This ritual has no connection to their entrance into the faith; it is instead based on the strict observance of cleanliness described by the prophet Muhammad as being a defining feature of appropriate Muslim behavior.