Mahabharata Adi Parva Chapter 100:3

Mahabharata Adi Parva Chapter 100:3 And having reached his city that was like unto the celestial capital, that monarch of Puru's line regarded himself greatly fortunate. And having summoned all the Pauravas together, for the protection of his kingdom he installed his son as his heir-apparent. And O bull of Bharata's race, the prince soon gratified by his behaviour his father and the other members of the Paurava race: in fact, all the subjects of the kingdom. And the king of incomparable prowess lived happily with that son of his. "Four years had thus passed away, when the king one day went into the woods on the bank of the Yamuna. And while the king was rambling there, he perceived a sweet scent coming from an unknown direction. And the monarch, impelled by the desire of ascertaining the cause, wandered hither and thither. And in course of his ramble, he beheld a black-eyed maiden of celestial beauty, the daughter of a fisherman. The king addressing her, said, 'Who art thou, and whose daughter? What dost thou do here, O timid one?' She answered, 'Blest be thou! I am the daughter of the chief of the fishermen. At his command, I am engaged for religious merit, in rowing passengers across this river in my boat.' And Santanu, beholding that maiden of celestial form endued with beauty, amiableness, and such fragrance, desired her for his wife. And repairing unto her father, the king solicited his consent to the proposed match. But the chief of the fishermen replied to the monarch, saying, 'O king, as soon as my daughter of superior complexion was born, it was of course, understood that she should be bestowed upon a husband. But listen to the desire I have cherished all along in my heart. O sinless one, thou art truthful: if thou desirest to obtain this maiden as a gift from me, give, me then this pledge. If, indeed, thou givest the pledge, I will of course bestow my daughter upon thee for truly I can never obtain a husband for her equal to thee.' "Santanu, hearing this, replied, 'When I have heard of the pledge thou askest, I shall then say whether I would be able to grant it. If it is capable of being granted, I shall certainly grant it. Otherwise how shall I grant it.' The fisherman said, 'O king, what I ask of thee is this: the son born of this maiden shall be installed by thee on thy throne and none else shall thou make thy successor.' "Vaisampayana continued, 'O Bharata, when Santanu heard this, he felt no inclination to grant such a boon, though the fire of desire sorely burnt him within. The king with his heart afflicted by desire returned to Hastinapura, thinking all the way of the fisherman's daughter. And having returned home, the monarch passed his time in sorrowful meditation. One day, Devavrata approaching his afflicted father said, 'All is prosperity with thee; all chiefs obey thee; then how is it that thou grievest thus? Absorbed in thy own thoughts, thou speakest not a word to me in reply.