Regarding the Verse: "And say not to anyone who offers you peace (by accepting Islam), You are not a believer." There was a man amidst his sheep. The Muslims pursued him, and he said (to them) "Peace be on you." But they killed him and took over his sheep. Thereupon Allah revealed in that concern, the above Verse up to:-- "...seeking the perishable good of this life." (4.94) i.e. those sheep.  

السَّلاَمُ عَلَيْكُمْ فَقَتَلُوهُ وَأَخَذُوا غُنَيْمَتَهُ فَأَنْزَلَ اللَّهُ فِي ذَلِكَ إِلَى قَوْلِهِ {عَرَضَ الْحَيَاةِ الدُّنْيَا} تِلْكَ الْغُنَيْمَةُ قَالَ قَرَأَ ابْنُ عَبَّاسٍ السَّلاَمَ  

As-Salam-o-'Alaikum. They caught hold of him and killed him and took possession of his flock. Then this verse was revealed:" He who meets you and extends you salutations, don't say: You are not a Muslim" (iv. 94). Ibn 'Abbas, however, recited the word as-Salam instead of" as-Salam".  

لَقِيَ نَاسٌ مِنَ الْمُسْلِمِينَ رَجُلاً فِي غُنَيْمَةٍ لَهُ فَقَالَ السَّلاَمُ عَلَيْكُمْ فَأَخَذُوهُ فَقَتَلُوهُ وَأَخَذُوا تِلْكَ الْغُنَيْمَةَ فَنَزَلَتْ { وَلاَ تَقُولُوا لِمَنْ أَلْقَى إِلَيْكُمُ السَّلَمَ لَسْتَ مُؤْمِنًا} وَقَرَأَهَا ابْنُ عَبَّاسٍ السَّلاَمَ  

The Muslims met a man with some sheep of his. He said: Peace be upon you. But they killed him and took those few sheep. Thereupon the following Qur'anic verse was revealed: "...And say to anyone who offers you a salutation: Thou art none of believer, coveting the perishable good of this life." meaning these few sheep.  

لَحِقَ الْمُسْلِمُونَ رَجُلاً فِي غُنَيْمَةٍ لَهُ فَقَالَ السَّلاَمُ عَلَيْكُمْ فَقَتَلُوهُ وَأَخَذُوا تِلْكَ الْغُنَيْمَةَ فَنَزَلَتْ { وَلاَ تَقُولُوا لِمَنْ أَلْقَى إِلَيْكُمُ السَّلاَمَ لَسْتَ مُؤْمِنًا تَبْتَغُونَ عَرَضَ الْحَيَاةِ الدُّنْيَا } تِلْكَ الْغُنَيْمَةَ  

"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)." (Using translation from Tirmidhī 3030)   

مَرَّ نَفَرٌ مِنْ أَصْحَابِ النَّبِيِّ ﷺ عَلَى رَجُلٍ مِنْ بَنِي سُلَيْمٍ مَعَهُ غَنَمٌ لَهُ فَسَلَّمَ عَلَيْهِمْ فَقَالُوا مَا سَلَّمَ عَلَيْكُمْ إِلَّا تَعَوُّذًا مِنْكُمْ فَعَمَدُوا إِلَيْهِ فَقَتَلُوهُ وَأَخَذُوا غَنَمَهُ فَأَتَوْا بِهَا النَّبِيَّ ﷺ فَأَنْزَلَ اللهُ تَبَارَكَ وَتَعَالَى {وَلَا تَقُولُوا لِمَنْ أَلْقَى إِلَيْكُمُ السَّلَامَ لَسْتَ مُؤْمِنًا تَبْتَغُونَ عَرَضَ الْحَيَاةِ الدُّنْيَا} [النساء 94] إِلَى آخِرِ الْآيَةِ  

The Muslims met a man with some sheep of his. He said: Peace be upon you. But they killed him and took those few sheep. Thereupon the following Qur'anic verse was revealed: "...And say to anyone who offers you a salutation: Thou art none of believer, coveting the perishable good of this life." meaning these few sheep. (Using translation from Abū Dāʾūd 3974)   

السَّلَامُ عَلَيْكُمْ فَقَتَلُوهُ وَأَخَذُوا غُنَيْمَتَهُ فَأَنْزَلَ اللهُ ﷻ {وَلَا تَقُولُوا لِمَنْ أَلْقَى إِلَيْكُمُ السَّلَامَ لَسْتَ مُؤْمِنًا تَبْتَغُونَ عَرَضَ الْحَيَاةِ الدُّنْيَا} [النساء 94] تِلْكَ الْغُنَيْمَةُ