Prohibited to lie

The Sultan was told by his teacher that lying was a great crime and should be banned. So the Sultan ordered his executioner to the city gate and told him to ask each person entering the city why he was visiting and execute any who lied.
Next morning the Mullah stood in line to go to the market in the city. The executioner asked him on the penalty of death, “Why are you entering the city?” The Mullah replied, “I am going to be executed!”