"Holy Teacher"--The Master while residing at Jetavana told this story, about the Fraternity of Six Priests. It is related in detail in the Vinaya. Here is a brief summary of it.
The Master sent for the Six Priests and asked if it were true that they taught the law from a low seat, while their pupils sat on a higher seat. They confessed that it was so, and the Master in reproving these brethren for their want of respect for his law, said that wise men of old had to rebuke men for teaching even heretical doctrines while sitting on a low seat. Then he told them an old story.
"Once upon a time when Brahmadatta reigned in Benares, the Bodhisattva came to life as the son of a pariah woman, and when he was grown up, he established himself as a householder. And his wife being with child had a great longing for the mango fruit, and said to her husband, 'My lord, I have a desire to eat mangoes.'
"'My dear,' he said, 'there are no mangoes at this season, I will bring you some other acid fruit.'
"'My lord,' said she, 'if I can have a mango, I shall live. Otherwise I shall die.'
"He being infatuated about his wife thought, 'Where in the world am I to get a mango?' Now at this time there was a mango tree in the garden of the king of Benares, which had fruit on it all the year round. So he thought, 'I will get a ripe mango there to appease her longings.' And going to the garden by night he climbed up the tree, and stepped from one branch to another, looking for the fruit, and while he was thus engaged, the day began to break. Thought he, 'If I shall come down now to go away, I shall be seen and seized as a thief. I will wait till it is dark.' So he climbed up into a fork of the tree and remained there, perched upon it.
"Now at this time the king of Benares was being taught sacred texts by his chaplain. And coming into the garden he sat down on a high seat at the foot of the mango tree, and placing his teacher on a lower seat, he had a lesson from him. The Bodhisattva sitting above them thought, 'How wicked this king is. He is learning the sacred texts, sitting on a high seat. The Brahmin too is equally wicked, to sit and teach him from a lower seat. I also am wicked, for I have fallen into the power of a woman, and counting my life as nought, I am stealing the mango fruit.' Then taking hold of a hanging bough, he let himself down from the tree, and stood before these two men and said, 'O Great King, I am a lost man, and thou a gross fool, and this priest is as one dead.' And being asked by the king what he meant by these words, he uttered the first stanza:--
"'Holy Teacher, Royal Scholar, lo! the sinful deed I saw,
"The Brahmin, on hearing this, repeated the second stanza:--
"'My food is pure rice from the hill,
"On hearing this the Bodhisattva recited two more stanzas:--
"'Brahmin, go range the length and breadth of earth;
"Then the king being pleased with his exposition of the law, asked him of what caste he was. 'I am a pariah, my lord,' he said. 'Friend,' he replied, 'had you been of a high caste family, I would have made you sole king. But henceforth I will be king by day, and you shall be king by night.' And with these words he placed upon his neck the wreath of flowers with which he himself was adorned, and made him lord protector over the city. And hence is derived the custom for the lords of the city to wear a wreath of red flowers on their neck. And from that day forward the king abiding in his admonition paid respect to his teacher, and learned sacred texts from him, sitting on a lower seat."
The Master, his lesson ended, identified the Birth: "At that time Ananda was the king, and I myself was the pariah."