I think I understood your question
and to know the answer first you must know what is "Islam" or "Muslim" means ?
The word "Islam" itself means "Submission to Allah." The religion of Islam is not named after a person as in the case of "Christianity" which was named after Jesus Christ, "Buddhism" after Gutama Buddha , "Marxism" after Karl Marx, and "Confucianism" after Confucius.
Similarly, Islam is not named after a tribe like "Judaism" after the tribe of Judah and "Hinduism" after the Hindus. The Arabic word "Islam" means the submission or surrender of one's will to the will of the only true god worthy of worship, "Allah" (known as God "the Father" in Christianity).
Anyone who does indeed submit to the will of Allah as required by Islam is termed a "Muslim," which means one who has submitted to the will of Allah. Many people in the West have developed the sad mis *******d trend of calling Islam "Muhammadenism" and it's followers "Muhammadins." This is a totally foreign word to Muslims and unrecognized by them. No Muslim has ever called his religion "Muhammadenism" or called himself a "Muhammadin."
NOT NEEDED
And because we as Muslims believe that all prophets came a unified message from God with different laws and codes that govern the followers of each prophet, but one parent is the worship of God alone
Therefore, we believe that all the prophets and their followers were Muslims
And These are some verses from the Koran shows what I mean :
002.132 And this was the legacy that Abraham left to his sons, and so did Jacob; "Oh my sons! God hath chosen the Faith for you; then die not except in the State of Submission (to Allah).
002.133 Were ye witnesses when Death appeared before Jacob? Behold, he said to his sons: "What will ye worship after me?" They said: "We shall worship Thy God and the God of thy fathers- of Abraham, Isma'il and Isaac,- the one (True) God: To Him we bow (in Islam)." ---
God said :
021.025 Not an apostle did We send before thee without this inspiration sent by Us to him: that there is no god but I; therefore worship and serve Me.
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002.285 The Apostle believeth in what hath been revealed to him from his Lord, as do the men of faith. Each one (of them) believeth in God, His angels, His books, and His apostles. "We make no distinction (they say) between one and another of His apostles." And they say: "We hear, and we obey: (We seek) Thy forgiveness, Our Lord, and to Thee is the end of all journeys."
002.286 On no soul doth God place a burden greater than it can bear. It gets every good that it earns, and it suffers every ill that it earns. (Pray): "Our Lord! Condemn us not if we forget or fall into error; Our Lord! Lay not on us a burden like that which Thou didst lay on those before us; Our Lord! Lay not on us a burden greater than we have strength to bear. Blot out our sins, and grant us forgiveness. Have mercy on us. Thou art our Protector; Help us against those who stand against faith."
I hope to be reconciled in the answer to your question