Question Regarding Takfeer
Rules or principles are not derived ved from the incidents. To call someone kafir one needs to know he denied a truth deliberately and he has no excuse. Secondly we have not been given a responsibility to determine if a person is a kafir or not a kafir. This is not our domain. In the above incident it was an expression of anger from Hazrat Umar seeing the actions of the person, as there were hypocrites and Umar associated him with them and the prophet calmed him down.