Surah Al-Mu'minun — Ayah 53 (23:53)

English translation (Saheeh International)

But they [i.e., the people] divided their religion among them into portions [i.e., sects] - each faction, in what it has,¹ rejoicing.

1. - Of beliefs, opinions, customs, etc.

Brief commentary

After they passed away, their followers were divided in religion and became sects and groups, with each group conceited in believing that whatever it believed in was the true acceptable religion according to Allah, disregarding the views of anyone else.