"I'm sorry, but I must say no," said Nasruddin. "The donkey is not here right now; I loaned him to my brother-in-law, and they haven't come back yet."
At just that moment, the donkey let out a loud bray from inside the stable.
Before his neighbor could say anything, Nasruddin gave him a hard look. "Who are you going to believe: me, or the donkey?"
Inspired by: This is Nasruddin Tale Type T0072.
Notes: In some versions of this story, Nasruddin goes on to add that anyone who would take the word of a donkey is not worthy of any kind of loan.