This is an old joke, and it's subject to parallel evolutions. When it's passed down orally the characters, their backgrounds, and plot details remain interchangeable so long as the joke remains alive. This is merely one iteration, and its appearance in written form does not give it authority over any other iteration. But this is how I tell it.
Once upon a time, an al-Qaeda terrorist convicted of murder escaped from a prison stationed in the middle of the Iraqi desert. He wandered the desert desperate for water, until he saw something in the distance.
As he approached it he made out its shape - a small wooden booth. He could make out a small, frail old Muslim man standing in the booth as he made his way closer to the little shop.
The little man had set up shop here in the desert at a small dusty crossroad. He was selling high quality ties in the small shade of his booth. The escaped prisoner staggered up to the little Muslim man and asked, "Do you have water?"
The little Muslim man replied, "I have no water. Would you like to buy a tie? They cost only five thousand dinar."
The escaped prisoner shouted hysterically, "Stupid little old Muslim peasant! I do not need such over-priced adornments. To hell with your ties. I need water!"
"Sorry, I have none, just ties - pure silk, only five thousand dinar."
"Bah! A curse on your ties! I ought to wrap one around your scrawny little old neck and choke the life out of you. But I must conserve my energy, and I must find water!"
"Alright," said the little Muslim man. "It does not matter that you do not want to buy a tie from me, or that you threaten my life. I will show you that I am bigger than that," as the little man pointed to his right.
"If you continue over that hill to the East for another four kilometers, you will find a restaurant. It has the finest food and all the ice-cold water you need. Go in peace."
Cursing him again, the desperate terrorist staggered over the hill and away.
Several hours later the man crawled back, nearly dead. He heaved and panted for another minute before he could gather himself to speak as he gasped,
"They won't let me in without a tie."