What is this, the proclamation of the days of jahiliya (ignorance)? They said: Messenger of Allah, there is nothing serious. The two young men fell into dispute and the one struck at the back of the other. Thereupon he (the Holy Prophet) said: Well, a person should help his brother whether he is an oppressor or an oppressed. If he is the oppressor he should prevent him from doing it, for that is his help; and if he is the oppressed he should be helped (against oppression).  

اقْتَتَلَ غُلاَمَانِ غُلاَمٌ مِنَ الْمُهَاجِرِينَ وَغُلاَمٌ مِنَ الأَنْصَارِ فَنَادَى الْمُهَاجِرُ أَوِ الْمُهَاجِرُونَ يَا لَلْمُهَاجِرِينَ وَنَادَى الأَنْصَارِيُّ يَا لَلأَنْصَارِ فَخَرَجَ رَسُولُ اللَّهِ ﷺ فَقَالَ مَا هَذَا دَعْوَى أَهْلِ الْجَاهِلِيَّةِ قَالُوا لاَ يَا رَسُولَ اللَّهِ إِلاَّ أَنَّ غُلاَمَيْنِ اقْتَتَلاَ فَكَسَعَ أَحَدُهُمَا الآخَرَ قَالَ فَلاَ بَأْسَ وَلْيَنْصُرِ الرَّجُلُ أَخَاهُ ظَالِمًا أَوْ مَظْلُومًا إِنْ كَانَ ظَالِمًا فَلْيَنْهَهُ فَإِنَّهُ لَهُ نَصْرٌ وَإِنْ كَانَ مَظْلُومًا فَلْيَنْصُرْهُ  

We were along with Messenger of Allah ﷺ in an expedition that a person from amongst the emigrants struck at the back of a person from the Ansir. The Ansiri said: O Ansar! And the Muhijir said: O Emigrants! Thereupon Messenger of Allah ﷺ said: What are these proclamations of the Days of Ignorance? They said: Messenger of Allah, a person from the emigrants struck at the back of an Ansari, whereupon he said: It is something disgusting. 'Abdullah b. Ubayy heard it and said: They have indeed done it. By Allah, when we would return to Medina the respectable amongst them (the Ansar) would turn away the mean (the emigrants). Thereupon 'Umar said: Permit me so that I should strike the neck of this hypocrite. But he (the Holy Prophet) said: Leave him, the people may not say that Muhammad kills his companions.  

سَمِعَ عَمْرٌو جَابِرَ بْنَ عَبْدِ اللَّهِ يَقُولُ كُنَّا مَعَ النَّبِيِّ ﷺ فِي غَزَاةٍ فَكَسَعَ رَجُلٌ مِنَ الْمُهَاجِرِينَ رَجُلاً مِنَ الأَنْصَارِ فَقَالَ الأَنْصَارِيُّ يَا لَلأَنْصَارِ وَقَالَ الْمُهَاجِرِيُّ يَا لَلْمُهَاجِرِينَ فَقَالَ رَسُولُ اللَّهِ ﷺ مَا بَالُ دَعْوَى الْجَاهِلِيَّةِ قَالُوا يَا رَسُولَ اللَّهِ كَسَعَ رَجُلٌ مِنَ الْمُهَاجِرِينَ رَجُلاً مِنَ الأَنْصَارِ فَقَالَ دَعُوهَا فَإِنَّهَا مُنْتِنَةٌ فَسَمِعَهَا عَبْدُ اللَّهِ بْنُ أُبَىٍّ فَقَالَ قَدْ فَعَلُوهَا وَاللَّهِ لَئِنْ رَجَعْنَا إِلَى الْمَدِينَةِ لَيُخْرِجَنَّ الأَعَزُّ مِنْهَا الأَذَلَّ قَالَ عُمَرُ دَعْنِي أَضْرِبْ عُنُقَ هَذَا الْمُنَافِقِ فَقَالَ دَعْهُ لاَ يَتَحَدَّثُ النَّاسُ أَنَّ مُحَمَّدًا يَقْتُلُ أَصْحَابَهُ  

Leave it. for it is something disgusting. Ibn Mansur said that in the narration transmitted on the authority of Amr (these words are also found):" I heard Jabir."  

كَسَعَ رَجُلٌ مِنَ الْمُهَاجِرِينَ رَجُلاً مِنَ الأَنْصَارِ فَأَتَى النَّبِيَّ ﷺ فَسَأَلَهُ الْقَوَدَ فَقَالَ النَّبِيُّ ﷺ دَعُوهَا فَإِنَّهَا مُنْتِنَةٌ قَالَ ابْنُ مَنْصُورٍ فِي رِوَايَتِهِ عَمْرٌو قَالَ سَمِعْتُ جَابِرًا