To be furious while preaching or teaching if one sees what one hates

Narrated Abu Musa: The Prophet (sallallahu 'alaihi wa sallam) was asked about things which he did not like, but when the questioners insisted, the Prophet got angry. He then said to the people, "Ask me anything you like." A man asked, "Who is my father?" The Prophet (sallallahu 'alaihi wa sallam) replied, "Your father is Hudhafa." Then another man got up and said, "Who is my father, O Allah's Messenger (sallallahu 'alaihi wa sallam) ?" He replied, "Your father is Salim, Maula (the freed slave) of Shaiba." So when `Umar saw that (the anger) on the face of the Prophet (sallallahu 'alaihi wa sallam) he said, "O Allah's Messenger (sallallahu 'alaihi wa sallam)! We repent to Allah (Our offending you).