Surah Ash-Shuraa 42:8

وَلَوْ شَآءَ ٱللَّهُ لَجَعَلَهُمْ أُمَّةً وَٰحِدَةً وَلَـٰكِن يُدْخِلُ مَن يَشَآءُ فِى رَحْمَتِهِۦ ۚ وَٱلظَّـٰلِمُونَ مَا لَهُم مِّن وَلِىٍّ وَلَا نَصِيرٍ

And if Allāh willed, He could have made them [of] one religion, but He admits whom He wills into His mercy. And the wrongdoers have not any protector or helper.

Translation: Saheeh International

Tafsir

And had God willed He would have made them one community in other words following one religion and that is Islam; but He admits whomever He will into His mercy and the evildoers the disbelievers have neither guardian nor helper to ward off the chastisement from them.

Excerpt from Tafsir al-Jalalayn, commentary on 42:8, via Quran.com. The reader has the full commentary and 9 more tafsirs.