Who is a Muslim?
A muslim is simply someone who has embraced Islam.
However, Islam is the universe’s religion, for Islam is nothing other than obedience and submission to God, the Lord of the universe. The sun, moon, Earth, and all heavenly bodies are Muslim, as are air, water, heat, stones, trees, and animals, for everything in existence obeys God by submitting to His laws. Even unbelievers and atheists are Muslim as far as their bodily existence is concerned, for each part of their bodies follows the course God established for it, from birth until death and dissolution. However, God has allowed all humans, free will, to accept or reject Islam, the natural teachings of humanity.
Islam is the religion which was given to Adam, the first man and the first prophet of Allah, and it was the religion of all the prophets sent by Allah to mankind , hence ALL PROPHETS WERE MUSLIM.