‘Abdullah bin ‘Abbaas (radhiyallahu ‘anhuma) mentions that a hypocrite by the name of Bishr once had an argument with a Jew. In order to resolve the argument, the Jew suggested that they resort to Rasulullah (sallallahu ‘alaihi wasallam) who would preside over their case and decide who was in the right. The hypocrite, on the other hand, suggested that they take the case to Ka’b bin Ashraf, a Jewish leader. They eventually took the case to Rasulullah (sallallahu ‘alaihi wasallam) who passed judgement in favour of the Jew against the hypocrite.
The hypocrite was unhappy with the decision and took the Jew to ‘Umar (radhiyallahu ‘anhu) for a “second opinion”. The Jew said to ‘Umar (radhiyallahu ‘anhu), “Rasulullah (sallallahu ‘alaihi wasallam) has already decided the case but he is not pleased with the decision of Rasulullah (sallallahu ‘alaihi wasallam).” ‘Umar (radhiyallahu ‘anhu) asked the hypocrite, “Is that so?” When he replied in the affirmative, ‘Umar (radhiyallahu ‘anhu) instructed them to stay where they were and that he would be with them soon. He then entered and brought his sword. As he emerged, he struck the neck of the hypocrite killing him. He then declared, “This is the decision I make for the one who is unhappy with the decision made by Allah Ta‘ala and His Rasul (sallallahu ‘alaihi wasallam).”
It was on this occasion that the verse “Have you not seen those who claim that they believed in what was revealed to you and what was revealed before you? They want to take their disputes to the Taaghut (i.e. Ka’b bin Ashraf), while they were ordered to reject him. Shaitaan wants to mislead them to a remote wrong way” was revealed. According to some narrations, Jibreel (‘alaihis salaam) came down and said, ‘Umar has differentiated between truth and falsehood. (Roohul Ma‘aani, vol. 5, pg. 88 and Tafseer Qurbtubi, vol. 6, pg. 436)