يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ عَلَيْكُمْ أَنفُسَكُمْ ۖ لَا يَضُرُّكُم مَّن ضَلَّ إِذَا ٱهْتَدَيْتُمْ ۚ إِلَى ٱللَّهِ مَرْجِعُكُمْ جَمِيعًا فَيُنَبِّئُكُم بِمَا كُنتُمْ تَعْمَلُونَ
Yaaa aiyuhal lazeena aamanoo 'alaikum anfusakum laa yadurrukum man dalla izah tadaitum; ilal laahi marji'ukum jamee'an fayunabbi'ukum bimaa kuntum ta'maloon
You who believe, take care of your own selves. Those who go astray cannot harm you if you are rightly guided. To God you will all return, and he will inform you of what you have been doing.
ʿAlaykum anfusakum is a fixed idiom of urging, a preposition and pronoun doing the work of a verb: take your own selves in hand. Commentators have long pulled the line in two directions, as leave to withdraw once others go astray, or as no leave at all, since being rightly guided was itself held to include calling others to what is right. Everything turns on that proviso.