This is probably the best known Nasrudin story. When I was an ESOL teacher this is one I always told to my students. It was some measure of their English listening skills if they could get the joke!
Can I Borrow Your Donkey?
“Can I borrow your donkey?” a neighbour asked Nasrudin at his door.
“I’d love to help you,” was the reply, “but I’ve already lent it to someone else.”
Just then, a loud “hee-haw” came from Nasrudin’s yard.
“Hey,” the man said, “I just heard the donkey make a noise from your yard!”
Nasrudin quickly retorted, “Who do you believe; me or my donkey!”