I'm sure about something now ;)

When Nasreddin walked in a public square with a flock of followers, a Sheikh approached and challenged him: "What gives you the authority to arrogate the role of a spiritual leader?"

Nasreddin laughed and proclaimed: "I can make people do whatever I want! For example, if I tell you to get off your horse, you will obey."
The Sheikh snorted and spake unto him: "Prove it!"
Mulla replied: "Sorry, I was in error. But if you get off, I can make you get onto the horse!"
The Sheikh jumped on the ground.
"Well", Nasreddin laughed, "you see? I told you I can make you get off your horse, and there you did!"
Angrily, the Sheikh stomped with his foot and jumped back on the horse again to ride off.
"Well, and now I've fulfilled my second promise! I've made you get back on your horse again."

QED.