Was Islam an existing religion before the advent of the Prophet, peace and blessings be upon him?

The religion of Islam is the only religion accepted by Allah for all prophets, as mentioned in the Qur’an concerning Noah, Abraham, Moses, and Jesus, peace be upon them. Islam is obedience to Allah at all times, even if the laws (shariahs) differed in some of their forms. Before the advent of Prophet Muhammad, peace and blessings be upon him, there were a few Christians adhering to the true religion of Jesus. Islam, in its specific sense, is the religion with which Muhammad, peace and blessings be upon him, was sent. The dispute over the Islam of the nations of Moses and Jesus is lexical; specific Islam pertains to the nation of Muhammad, while general Islam encompasses the obedience of every nation to its prophet.