Bukhari Collection: ::Book Number 4:: Hadith # 720
Narrated Jabir:We were in the company of the Prophet in a Ghazwa. A large number of emigrants joined him and among the emigrants there was a person who used to play jokes (or play with spears); so he (jokingly) stroked an Ansari man on the hip. The Ans-ari got so angry that both of them called their people. The Ansari said, "Help, O Ansar!" And the emigrant said "Help, O emigrants!" The Prophet came out and said, "What is wrong with the people (as they are calling) this call of the period of Ignorance? "Then he said, "What is the matter with them?" So he was told about the stroke of the emigrant to the Ansari. The Prophet said, "Stop this (i.e. appeal for help) for it is an evil call. "Abdullah bin Ubai bin Salul (a hypocrite) said, "The emigrants have called and (gathered against us); so when we return to Medina, surely, the more honorable people will expel therefrom the meaner," Upon that `Umar said, "O Allah's Prophet! Shall we not kill this evil person (i.e. `Abdullah bin Ubai bin Salul) ?" The Prophet) said, "(No), lest the people should say that Muhammad used to kill his companions."