The Bodhisatta was once a monkey. A farmer’s oxen had wandered off into the forest while he worked in his field with a spade. Overcome with grief, he searched for seven days without stopping even to eat, but couldn’t find them and got hopelessly lost deep in the Himalayas. Eventually he climbed a Malabar ebony tree to eat the fruit, but a branch broke and he fell into a pond at the bottom of a deep, hell-like gorge. After ten days, the Bodhisatta saw the man and carried him out on his back.
After the rescue, the Bodhisatta was exhausted and took a nap. The farmer, ravished by hunger, smashed the Bodhisatta’s head with a rock to kill and eat him. But the farmer was so weak he only injured him. The Bodhisatta, covered in blood and in great pain, sprang up into the safety of a high branch. Instead of getting angry he told the farmer he would walk in the treetops to lead him out of the forest.
Because of his sin against the Bodhisatta, the man became a wretched leper, mere skin and bones and always in pain. For seven years he wandered to and fro. One day as the man rested in a park, the king came there and asked what sinful deed he did to bring such suffering upon himself. The man told the king his whole story, and as it came to an end, the earth opened up and swallowed him into hell. So the king went home.
In the Lifetime of the Buddha
The leper was an earlier birth of Devadatta, a disciple of the Buddha who became his nemesis. When the Buddha heard some of his disciples discussing the time Devadatta had tried to kill him by rolling a boulder down a hill he told them this story so they knew Devadatta had also tried to kill him with a stone in the past.