10:19
وَمَا كَانَ ٱلنَّاسُ إِلَّآ أُمَّةً وَٰحِدَةً فَٱخْتَلَفُوا۟ ۚ وَلَوْلَا كَلِمَةٌ سَبَقَتْ مِن رَّبِّكَ لَقُضِىَ بَيْنَهُمْ فِيمَا فِيهِ يَخْتَلِفُونَ
wamā kāna l-nāsu illā ummatan wāḥidatan fa-ikh'talafū walawlā kalimatun sabaqat min rabbika laquḍiya baynahum fīmā fīhi yakhtalifūna
All people were originally one single community, but later they differed. If it had not been for a word from your Lord, the preordained judgement would already have been passed between them regarding their differences.
Mankind were but one community (i.e. on one religion - Islâmic Monotheism), then they differed (later); and had not it been for a Word that went forth before from your Lord, it would have been settled between them regarding what they differed.