Mbh 13.10.4c

Both of them began to grow and both acquired great knowledge in the usual branches of study. The Brahmana became well versed in the Vedas as also in the Atharvans.[23] In the matter, again of all sacrifices ordained in the Sutras, of that Vedanga which deals with religious rites and observances, astrology and astronomy the reborn Rishi attained great excellence. In the Sankhya philosophy too he began to take great delight. Meanwhile, the reborn Sudra who had become a prince, when his father, the king died, performed his last rites; and after he had purified himself by accomplishing all the obsequial ceremonies, he was installed by the subjects of his father as their king on his paternal throne. But soon after his own installation as king, he installed the reborn Rishi as his priest. Indeed, having made the Brahmana his priest, the king began to pass his days in great happiness. He ruled his kingdom righteously and protected and cherished all his subjects. Everyday, however, the king on the occasion of receiving benedictions from his priest as also of the performance of religious and other sacred rites, smiled or laughed at him loudly. In this way, O monarch, the reborn Sudra who had become a king, laughed at sight of his priest on numberless occasions.[24] The priest, marking that the king always smiled or laughed whenever he happened to cast his eyes on him, became angry. On one occasion he met the king in a place where there was nobody else. He pleased the king by agreeable discourse. Taking advantage of that moment, O chief of Bharata's race, the priest addressed the king, saying,--'O thou of great splendour, I pray thee to grant me a single boon.'