What religion did the Prophet 
follow before the revelation?
Answer:
The Prophet of Allah was the follower of “Deen Hanif”, which was basically a monotheistic creed, ascribing to the belief of “one God” and adhering to the monotheistic practices of the Abrahamic religion which included Salah, Fasting, Hajj, Tawaf and Itikaaf.
Allah 
in the Holy Qur’an has said:
“Say (O Muhammad ): “O you mankind! If you are in doubt as to my religion (Islam), then (know that) I will never worship those whom you worship, besides Allah. But I worship Allah Who causes you to die, I am commanded to be one of the believers. And (it is revealed to me): Direct your face (O Muhammad ) entirely towards the Deen Hanif (Islamic Monotheism) and never be one those who ascribe partners to Allah.” (Surah Yunus v.104-v.105)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham