On the 12th Rabiul-Awal of the Hijri lunar calendar, according to Sunni traditions, the Islamic world begins celebrating the anniversary of the birth of the Messenger of Allah, the Prophet Muhammad. It is on this day that the Week of Unity in Islam begins, which ends on the 17th of Rabi'ul-Awal, when the anniversary of the birth of the Prophet Muhammad is celebrated according to Shia traditions. The Week of Unity in Islam is a holiday dedicated to the unity of Sunni and Shiite Muslims. The initiator of the Week of Unity in Islam was the great Ayatollah Khomeini. Since followers of Shiism believe that the Prophet Muhammad was born on the 17th of Rabi al-Awwal, and the Sunnis celebrate this holiday on the 12th of Rabi al-Awwal, Grand Ayatollah Khomeini proposed to call the interval between these two dates the Week of Unity in Islam.