The Quran Verse
Surah 30:30:
So set your face toward the religion... the Fitra of Allah upon which He has created mankind. No change should there be in the creation of Allah...
This verse introduces the concept that every human is born a "natural monotheist" (a Muslim).
This is the Islamic counter-polemic to the Christian doctrine of Original Sin.
If monotheism is the "unchangeable creation of Allah," then why is the world full of polytheists? Critics argue this creates a logical tension: if Allah's creation cannot be changed, yet most humans are "corrupted" by their parents into other faiths (as per the Hadith), then the "unchangeable" nature of Allah has, in fact, been changed by human intervention.