Abraham (peace be upon him) was a pure Muslim

Tell them: "O people of the Book, let us come to an agreement on that which is common between us, that we worship no one but God, and make none His compeer, and that none of us take any others for lord apart from God." If they turn away you tell them: "Bear witness that we submit to Him."

O people of the Book, why dispute about Abraham? The Torah and the Gospel were sent down after him: Do you not understand?

Remember you are those who disputed the things you knew; so wherefore dispute about things you do not know? And God has the knowledge, while you do not know.

Neither was Abraham a Jew nor a Christian, but upright and obedient, and not an idolater.

Of all men the nearest to Abraham are those who follow him, and then this Prophet and the faithful; and God is the protector of all believers.