Answer: Abu Bakr and Ali
Explanation: Two candidates who were competing for the post of Muhammad after his death were two representatives of the two sects of Islam. The question of Muhammad's successor caused a split among the Muslims, because they differed in terms of how he was to be chosen. Thus the Sunni Muslims thought that anyone capable enough could be the heir, i.e. the caliph, in this case, Abu Bakr, while the Shia Muslims thought that this must be Muhammad's cousin, that is, Ali.