One day Nasreddin went to town to buy new clothes. First he tried on a pair of trousers. He didn't like the trousers, so he gave them back to the shopkeeper. Then he tried a robe which had the same price as the trousers. Nasreddin was pleased with the robe, and he left the shop. Before he climbed on his donkey to ride home, the shopkeeper and the shop-assistant ran out.
"You didn't pay for the robe!" said the shopkeeper.
"But I gave you the trousers in exchange for the robe, didn't I?" replied Nasreddin.
"Yes, but you didn't pay for the trousers, either!" said the shopkeeper.
"But I didn't buy the trousers," replied Nasreddin. "I am not so stupid as to pay for something which I never bought."