When the Holy Prophet came to Madina all the people except the Jews were converted to Islam. Most of them were sincere and earnest in their faith in Islam. Some of them in spite of their profession of Islam were hypocrites and indulge in activities hostile to Islam. There were some among them on whom Islam sat lightly and who did not fully realise the spirit of Islam or the status of the Holy Prophet.
It is recorded on the authority of Abul Aswad that two persons of Madina who professed Islam but did not realise its full significance had a dispute among themselves and took the matter to the Holy Prophet for decision. After hearing both the parties, the Holy Prophet gave his decision in favour of one person. The other person felt dissatisfied, and at his instance both of them went to Umar and the aggrieved person lodged an appeal with Umar against the decision of the Holy Prophet.
After hearing both the parties, Umar said to the man who had filed the appeal: "So you are dissatisfied with the decision of the Holy Prophet, and want me to reverse his decision."
"Yes, that is so," said the man
"And are you a Muslim," enquired Umar.
The man said, "Yes, I am."
Thereupon Umar said, "Wait for a while. I will soon give my decision that would satisfy you."
Umar went inside the house and brought his sword. With the sword Umar smote the appellant saying, "Woe to you, you regard yourself a Muslim and yet choose to appeal to me against the decision of the Holy Prophet. You are an infidel, and the penalty for your infidelity is death."
The other man went to the Holy Prophet and complained that Umar had killed his companion.
The Holy Prophet summoned Umar and put him to explanation. Umar said, "The man wanted me to hear an appeal against the decision of the Holy Prophet, and for this impudence he deserved the punishment of death."
The Holy Prophet deferred the decision on the case till God gave some light on the matter.
Soon God revealed that he who had no confidence in the Holy Prophet was no believer. As such Umar was justified in killing the man who had by his action expressed want of faith in the Holy Prophet.
The Holy Prophet accordingly absolved Umar of the charge of murdering a believer.