The Bodhisatta was once a brahmin. It was the custom in a town for locals drawing water from a well to make merit by pouring some water in a trough for animals. One day when the Bodhisatta stopped at the well to drink, he saw a monkey sitting and watching him and then noticed the water trough was empty. He filled it and sat down under a tree to watch the monkey.
After it had a drink, the monkey grimaced to try to frighten the Bodhisatta. The Bodhisatta called the ungrateful monkey wicked and said he was not bothered by just making a face. The monkey replied, “Do you think that’s I all I can do? Next I am going to take a dump on your head before I leave.” Hearing this, the Bodhisatta got up to go, but the monkey was quick and it jumped into a branch and did as it said it would before running off into the forest shrieking loudly. The Bodhisatta washed and went his way.
In the Lifetime of the Buddha
The monkey was an earlier birth of Devadatta, a disciple of the Buddha who became his nemesis. One day the disciples were discussing Devadatta’s ingratitude and treachery and the Buddha told this story to let them know that Devadatta had been this same way in the past.