A poor fisherman cast his net and pulled up a great fish. As he lifted it from the water, the fish spoke. Cut me open, it said. Gather my blood in three bottles. Keep them safely. You will marry, and your wife will bear you three sons at once. Whenever one of the three is in danger, the blood in his bottle will change color.
The fisherman obeyed. In time his wife gave birth to triplets so identical that no one could tell them apart. Even their parents could not mark which boy was which. They grew up together and became men.
The eldest set out to seek his fortune. He came to a town being terrorized by a lion that devoured the young women. The king had promised his daughter to whoever killed the beast. The young man did not know about the offer. He found the lion, fought it, and killed it in the woods. Then he walked on.
An old man who had watched the fight from a hiding place took the lion's head, carried it to the court, and claimed the bounty. The king prepared to give his daughter to the impostor. The real hero heard the proclamation in a neighboring town, returned, exposed the old man's lie, and married the princess.
One day, from the palace window, he saw a distant building and asked what it was. That is the house of a sorceress, he was told. Anyone who enters never comes out. He rode there. An old woman was sitting by a great fire complaining that she was cold. She asked him to pluck a hair from the black dog sitting beside her and throw it into the fire. As soon as his hand touched the hair, ropes rose up and bound him. A wizard appeared and locked him in a chamber.
Back at the fisherman's home the first bottle of blood went dark. The father sent the second brother to search. The princess, deceived by the identical appearance of the brothers, treated him as her husband and told him what had happened. He too rode to the sorceress's palace and fell into the same trap. The second bottle darkened.
The father sent the third brother. He brought a dog and a horse of his own. At the gate, he tied them outside. He entered the palace. The old woman asked him to pluck a hair from her dog. He pretended to comply, but instead plucked a hair from his own dog, and threw that into the fire. The spell shattered. He drew his sword, killed the sorceress, broke into the chamber, and found his two brothers imprisoned with dozens of other captives. He freed them all. The reunited brothers returned to the princess. The eldest recognized her as his wife. The father at home saw the three bottles of blood turn bright red again. He went to find them, and they all lived happily together.
This remarkable Jewish folk tale from Codex Gaster 130, preserved in The Exempla of the Rabbis (Gaster, 1924), is one of many medieval Jewish versions of the widespread Two Brothers folk pattern. It teaches that cleverness saves where brute obedience fails. A borrowed hair will not break the spell. Only what is truly yours will.