This assumption is not correct.
People at the start, at the time of Adam, were on one religion worshipping God alone, without any associate or equal.
In other words, Adam was a prophet of God. Adam together with his sons served God Almighty: the Creator.
Then, afterwards, they fell into idolatry and associating some peers or equals with God.
Therefore, God sent them many apostles to warn them of severe punishment if they keep up their idolatry and association, and to give the glad tidings for those who exclusively serve Him alone and do not associate with Him any one or any thing.
God – be exalted – said in the Quran 2: 213
كَانَ النَّاسُ أُمَّةً وَاحِدَةً فَبَعَثَ اللّهُ النَّبِيِّينَ مُبَشِّرِينَ وَمُنذِرِينَ وَأَنزَلَ مَعَهُمُ الْكِتَابَ بِالْحَقِّ لِيَحْكُمَ بَيْنَ النَّاسِ فِيمَا اخْتَلَفُواْ فِيهِ وَمَا اخْتَلَفَ فِيهِ إِلاَّ الَّذِينَ أُوتُوهُ مِن بَعْدِ مَا جَاءتْهُمُ الْبَيِّنَاتُ بَغْيًا بَيْنَهُمْ فَهَدَى اللّهُ الَّذِينَ آمَنُواْ لِمَا اخْتَلَفُواْ فِيهِ مِنَ الْحَقِّ بِإِذْنِهِ وَاللّهُ يَهْدِي مَن يَشَاء إِلَى صِرَاطٍ مُّسْتَقِيمٍ
The explanation: (People were one community [of monotheists],
and God sent prophets with the glad tidings and the warning, and sent down the [Heavenly] Scripture with them, indicating the true [religion]; that the [prophet] might judge people concerning their deviation [from monotheism];
but none deviated therefrom save those [religious leaders] given the [Scripture] even after the manifest [signs] had come to them, due to their 'greed and their wronging each other';
so God, with His permission, guided the believers to the truth from which they deviated; for God guides whom He pleases to a standard path [of monotheism.] )