At one point in their history Sikhs were either hindus or muslims

There religious teaCHER declared himself as a prophet of sorts and

Now an interesting fact
Adi gRanth takes most of its principles from the Quran, so its no biggy that it mentions the Big bang and the round earth(though in the Quran the shape is of a sphere which is more correct) etc.

The book was compiled by studying the faith of islam with two of his muslim friends namely Sheikh Farid, and Kabir.

He never claimed divinity though but installed the principle of One God (Same as Islam) and the priesthood (Not important in Islam atall).