A Sufi master traveling alone through a desolate mountain region was suddenly faced by an ogre–a giant ghoul, who told him that he was going to destroy him. The master said, "Very well, try if you like, but I can overcome you, for I am immensely powerful in more ways than you think."
"Nonsense," said the ghoul "You are a Sufi master, interested in spiritual things. You cannot overcome me, because I rely upon brute force, and I am thirty times larger than you."
"If you want a trial of strength," said the Sufi, "take this stone and squeeze liquid out of it." He picked up a small piece of rock and handed it to the apparition. Try as he might, the ghoul could not. "It is impossible; there is no water in this stone. You show me if there is."
In the half-darkness, the master took the stone, took an egg out of his pocket, and squeezed the two together, holding his hand over that of the ghoul. The ghoul was impressed; for people are often impressed by things that they do not understand, and value such things highly, more highly than they should in their own interests.
"I must think this over," he said. "Come to my cave, and I shall give you hospitality for the night." The Sufi accompanied him to an immense cave, strewn with the belongings of thousands of murdered travelers, a veritable Aladdin's cavern. "Lie here beside me and sleep," said the ghoul, "and we will try conclusions in the morning." He lay down and immediately fell asleep.
The master, instinctively warned of treachery, suddenly felt a prompting to get up and conceal himself at some distance from the ghoul. This he did, after arranging the bed to give the impression that he was still in it.
No sooner was he sat a safe distance than the ghoul awoke. He picked up a tree-trunk with one hand, and dealt the dummy in the bed seven mighty blows. Then he lay down again and went to sleep. The master returned to his bed, lay down, and called to the ghoul:
"O ghoul! This cavern of yours is comfortable, but I have been bitten seven times by a mosquito. You really should do something about it."
This shocked the ghoul so much that he dared not attempt a further attack. After all, if a man had been hit seven times by a ghoul wielding a tree trunk with all the force he had... ?
In the morning the ghoul threw the Sufi a whole ox-skin and said: "Bring some water for breakfast, so that we can make tea." Instead of picking up the skin (which he could hardly have lifted in any case) the master walked to the near-by stream and started to dig a small channel towards the cave.
The ghoul was getting thirsty: "Why don't you bring the water?" "Patience, my friend. I am making a permanent channel to bring the spring-water right to the mouth of the cavern, so that you will never have to carry a water-skin."
But the ghoul was too thirsty to wait. PIcking up the skin, he strode to the river and filled it himself. When the tea was made he drank several gallons, and his reasoning faculties began to work a little better. "If you are so strong—and you have given me proof of it—why can't you dig that channel faster, instead of inch by inch?"
"Because," said the master, "nothing which is truly worth doing can be properly done without the expenditure of a minimum amount of effort. Everything has its own quantity of effort; and I am applying the minimum effort necessary to the digging of the canal.
Besides, I knew that you are such a creature of habit that you will always use the ox-skin."