The initial basis for Islam's unity--which from AD 625 took only one century to spread across Persia to the east and the Mediterranean Levant, Africa, and Europe to the west--was the Islamic scripture, the holy Quran. It consists of revelations made by Allah to Muhammad and asks for guidance: Guide us to the straight Way, the Way of those on whom you have bestowed Your Grace, not (the way) of those who earned Your Anger (such as the Jews), nor of those who went astray (such as the Christians) (Quran, Al-FGtihah 6-7).
The major preoccupation of doctrinaire Islam is living by God's will. The major ways of doing so involve "religious and social duties" (Ruthven, 2000, p. 79), which are contained in Islam's five pillars of wisdom:
Shahada. Reciting the basic declaration of faith.
Salat. Worship performed five times daily--dawn, noon, midafternoon, sunset, evening. Congregations gather in mosques on Fridays at noon.