There are two main groups in Islam, and Sunni Islam holds the most significant percentage of Islam. Its name comes from Sunnah, which refers to the activities and manners of the Prophet Muhammad. Sunni Muslims believe that the successor to the Prophet must be up to the task, and they have to be sincere and hardworking. Sunni Muslims are said to have chosen Abu Bakr without telling people who were close to Muhammed.
Shia Muslims are the second largest group of Islam. Shia Islam procured their name from the well-known phrase, "Shi'atu Ali," which means followers of Ali. They believe that a prophet is appointed by God alone, and the decision of who to choose next is the successor to his Prophet. Shia believes that Ali was chosen by God to be Muhammad's succession. The difference between the two came to fruition because of their disagreement over the succession of Muhammad.