Musnad Ahmad 33:1106

Husayn ibn Muhammad narrated to us, Sufyan—meaning Ibn ‘Uyaynah—narrated to us, from ‘Amr, who said: I heard Jabir ibn ‘Abdullah saying: We were with the Messenger of Allah (peace and blessings of Allah be upon him) on a military expedition—he said: They believe it was the expedition of Banu al-Mustaliq—when a man from the Emigrants (Muhajirun) kicked a man from the Helpers (Ansar). The Ansari said: "O for the Ansar!" And the Muhajir said: "O for the Muhajirun!" The Prophet (peace and blessings of Allah be upon him) heard that and said: "What is this call of the pre-Islamic era (Jahiliyyah)?" It was said: A man from the Muhajirun kicked a man from the Ansar. The Prophet (peace and blessings of Allah be upon him) said: "Leave it, for it is foul." Jabir said: The Muhajirun were fewer than the Ansar when they arrived in Medina, then the Muhajirun increased in number. This reached ‘Abdullah ibn Ubayy, so he said: "Have they done it? By Allah, if we return to Medina, the more honorable will surely drive out the more abased from it." ‘Umar heard that and came to the Prophet (peace and blessings of Allah be upon him) and said: "O Messenger of Allah, let me strike the neck of this hypocrite." The Prophet (peace and blessings of Allah be upon him) said: "O ‘Umar, leave him, lest the people say that Muhammad kills his companions."