Or were you witnesses when death approached Jacob, when he said to his sons, "What will you worship after me?" They said, "We will worship your God and the God of your fathers, Abraham and Ishmael and Isaac - one God. And we are Muslims [in submission] to Him."
Say, [O believers], "We have believed in Allah and what has been revealed to us and what has been revealed to Abraham and Ishmael and Isaac and Jacob and the Descendants and what was given to Moses and Jesus and what was given to the prophets from their Lord. We make no distinction between any of them, and we are Muslims [in submission] to Him."
So if they believe in the same as you believe in, then they have been [rightly] guided; but if they turn away, they are only in dissension, and Allah will be sufficient for you against them. And He is the Hearing, the Knowing.