The Battle of Siffin was fought in 657 CE between the forces of Ali, the fourth caliph of Islam, and Muawiyah, the governor of Syria. The battle ended in a stalemate, and a group of Ali's supporters, known as the Khawarij, split from his camp, accusing him of compromising with Muawiyah and violating Islamic principles.
Therefore, the correct answer is Khawarij, as the Battle of Siffin led to the emergence of this group in the early Islamic history.