Complex sentence: Recognizing Muhammad as God's true messenger is one of the central requirements in Islam which is clearly laid down in the second part of Shahadah, the Islamic proclamation of faith: "There is no god but Allah, and Muhammad is the Messenger of Allah".
Split into simpler sentences: Recognizing Muhammad as God's true messenger is one of the central requirements in Islam which is clearly laid down in the second part of Shahadah--the proclamation of Islamic faith. The Shahadah reads "There is no God but Allah, and Muhammad is the Messenger of Allah".