Muslims believe that Islam was the religion of the first human being, our father, Adam (Peace and Blessings be upon him). If one looks at it from a linguistic point of view, Islam means “submission.” One who submits their will to Allah would then be called a Muslim. Therefore, Muslims believe all The Honorable Prophets (Peace and Blessings be upon them all) were Muslims, including Noah, Abraham, Moses, Jesus, etc. Additionally, the people who followed their Prophet’s teachings at that time and submitted to Allah by accepting their message, they would also be called Muslims. This is something unique about Islam, and that is that it is not dependent on one human being. Christianity began with Christ, Judaism began with Judah, Buddhism began with Buddha, but Islam did not start with the Prophet Muhammad (Peace and Blessings be upon him). It is the religion that our Creator has ordained for us since the beginning of mankind.
And Allah Knows best.