<human>:  When did the split occur between Shia and Sunni islam?
<bot>: The split occurred in 632 AD. The split was caused by the death of the prophet Muhammad. After the death of Muhammad, Muslims began to split into two groups. The majority of Muslims are Shia Muslims, and they believe that Muhammad's son-in-law Ali was the first caliph. Shia Muslims believe that the caliphate should be passed down through the descendants of Ali, and that the caliph should be chosen by the majority of Muslims.