It is a supremacy of Islam that it is a religion of all prophets from Adam to the Last and Final Prophet Muhammad (peace & blessings of Allah be upon them). All prophets were the preachers and followers of Islam.

They not only spent their lives according to the teachings of this religion, but also they preached and advised their nations to accept Islam and follow its commandments and teachings, surrendering all their self-desires to will of one and only God “Allah”, .

It means shariah and teachings were different because of the different standard of living in different ages, but the roots and principles of religion were always remain the same. That’s why, once the Beloved Prophet Muhammad (peace & blessings of Allah be upon them) indicated to this:

‏ أَنَا أَوْلَى النَّاسِ بِعِيسَى ابْنِ مَرْيَمَ فِي الدُّنْيَا وَالآخِرَةِ، وَالأَنْبِيَاءُ إِخْوَةٌ لِعَلاَّتٍ، أُمَّهَاتُهُمْ شَتَّى، وَدِينُهُمْ وَاحِدٌ ‏”‏‏”
[صحیح البخاری: 3443]

“Both in this world and in the Hereafter, I am the nearest of all the people to Jesus, the son of Mary.
The prophets are paternal brothers; their mothers are different, but their religion is one.

Prophet Abraham and Ismail (peace & blessings of Allah be upon them) :

It is mentioned in the Holy Quran that prophet Abraham & prophet Ismail (peace & blessings of Allah be upon them)
commanded their descendants to follow this religion:

 اِذْ قَالَ لَهٗ رَبُّهٗٓ اَسْلِمْ ۙ قَالَ اَسْلَمْتُ لِرَبِّ الْعٰلَمِيْنَ

Behold! his Lord said to him: “Bow (thy will to Me):” He said: “I bow (my will) to the Lord and Cherisher of
the Universe.” (Holy Quran, 2:131)

وَوَصّٰى بِهَآ اِبْرٰھٖمُ بَنِيْهِ وَيَعْقُوْبُ ۭيٰبَنِىَّ اِنَّ اللّٰهَ اصْطَفٰى لَكُمُ الدِّيْنَ فَلَا تَمُوْتُنَّ اِلَّا وَاَنْتُمْ مُّسْلِمُوْنَ

And this was the legacy that Abraham left to his sons, and so did Jacob; “Oh my sons! Allah hath
chosen the Faith for you; then die not except in the Faith of Islam.” (Quran 2:131-132)

Prophet Moses (peace & blessings of Allah be upon him)

Prophet Moses (Peace & Blessings of Allah be upon him) had the same religion:

وَقَالَ مُوْسٰى يٰقَوْمِ اِنْ كُنْتُمْ اٰمَنْتُمْ بِاللّٰهِ فَعَلَيْهِ تَوَكَّلُوْٓا اِنْ كُنْتُمْ مُّسْلِمِيْنَ

Moses said: “O my people! If ye do (really) believe in Allah, then in Him put your trust if ye submit (your
will to His).” (Holy Quran 10:84)

Prophet Yousuf (Peace & Blessings of Allah be upon him)

Prophet Yousuf (Peace & Blessings of Allah be upon him) also prayed to die believing in Islam:

 رَبِّ قَدْ اٰتَيْتَنِيْ مِنَ الْمُلْكِ وَعَلَّمْتَنِيْ مِنْ تَاْوِيْلِ الْاَحَادِيْثِ فَاطِرَ السَّمٰوٰتِ وَالْاَرْضِ اَنْتَ وَلِيّٖ فِي الدُّنْيَا وَالْاٰخِرَةِ تَوَفَّنِيْ مُسْلِمًا وَّاَلْحِقْنِيْ

“O my Lord! Thou hast indeed bestowed on me some power, and taught me something of the interpretation of dreams and events,- O Thou Creator of the heavens and the earth! Thou art my Protector in this world and in the Hereafter. Take Thou my soul (at death) as one submitting to Thy will (as a Muslim), and unite me with the righteous.” (Quran 12:101)

Prophet Jesus (Peace & Blessings of Allah be upon him)

Prophet Jesus (Peace & Blessings of Allah be upon him) said, when he saw the disobedience of his followers:

فَلَمَّآ اَحَسَّ عِيْسٰى مِنْھُمُ الْكُفْرَ قَالَ مَنْ اَنْصَارِيْٓ اِلَى اللّٰهِ قَالَ الْحَوَارِيُّوْنَ نَحْنُ اَنْصَارُ اللّٰهِ اٰمَنَّا بِاللّٰهِ وَاشْهَدْ بِاَنَّا مُسْلِمُوْنَ

When Jesus found Unbelief on their part He said: “Who will be My helpers to (the work
of) Allah.” Said the disciples: “We are Allah.s helpers: We believe in Allah, and do thou bear
witness that we are Muslims. (Quran 3:52)

These all verses prove that Islam was the religion of all prophets (Peace & Blessings of Allah be upon them) and
they all were muslims. The Holy Prophet Muhammad (Peace & Blessings of Allah be upon him) was sent as the
seal of all prophets for finalization of this religion. He presented the complete mechanisms for living a
better life according to the revelation of Almighty Allah. This complete code of life is Islam what
Allah Almighty chosen for the whole humanity:

 اِنَّ الدِّيْنَ عِنْدَ اللّٰهِ الْاِسْلَامُ

The Religion before Allah is Islam (submission to His Will). (Quran 3:19)