"A man from Banu Sulaim who had some sheep with him, passed by some of the Companions of the Messenger of Allah ﷺ. He gave Salam to them and they said: 'He did not give Salam except to protect himself.' So they attacked him, killed him, and took his sheep. They went to the Messenger of Allah ﷺ with them, and Allah, Most High, revealed: O you who believe! When you go in the cause of Allah, verify and say not to anyone who greets you: "You are not a believer (4:94)."
مَرَّ رَجُلٌ مِنْ بَنِي سُلَيْمٍ عَلَى نَفَرٍ مِنْ أَصْحَابِ رَسُولِ اللَّهِ ﷺ وَمَعَهُ غَنَمٌ لَهُ فَسَلَّمَ عَلَيْهِمْ قَالُوا مَا سَلَّمَ عَلَيْكُمْ إِلاَّ لِيَتَعَوَّذَ مِنْكُمْ فَقَامُوا فَقَتَلُوهُ وَأَخَذُوا غَنَمَهُ فَأَتَوْا بِهَا رَسُولَ اللَّهِ ﷺ فَأَنْزَلَ اللَّهُ تَعَالَى ( يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا ضَرَبْتُمْ فِي سَبِيلِ اللَّهِ فَتَبَيَّنُوا وَلاَ تَقُولُوا لِمَنْ أَلْقَى إِلَيْكُمُ السَّلاَمَ لَسْتَ مُؤْمِنًا )