Mahabharata Adi Parva Chapter 100:5

Mahabharata Adi Parva Chapter 100:5 But I have something to tell thee. If the bride's father was Indra himself, even then he would have to repent of rejecting such an exceedingly honourable and desirable proposal of marriage. The great man of whose seed this celebrated maiden named Satyavati was born, is, indeed, equal to you in virtue. He hath spoken to me on many occasions of the virtues of thy father and told me that, the king alone is worthy of (marrying) Satyavati. Let me tell you that I have even rejected the solicitations of that best of Brahmarshis—the celestial sage Asita—who, too, had often asked for Satyavati's hand in marriage. I have only one word to say on the part of this maiden. In the matter of the proposed marriage there is one great objection founded on the fact of a rival in the person of a co-wife's son. O oppressor of all foes, he hath no security, even if he be an Asura or a Gandharva, who hath a rival in thee. There is this only objection to the proposed marriage, and nothing else. Blest be thou! But this is all I have to say in the matter of the bestowal or otherwise, of Satyavati.' "Vaisampayana continued, 'O thou of Bharata's race, Devavrata, having heard these words, and moved by the desire of benefiting his father thus answered in the hearing of the assembled chiefs, 'O foremost of truthful men, listen to the vow I utter! The man has not been or will not be born, who will have the courage to take such a vow! I shall accomplish all that thou demandest! The son that may be born of this maiden shall be our king.' Thus addressed, the chief of the fishermen, impelled by desire of sovereignty (for his daughter's son), to achieve the almost impossible, then said, 'O thou of virtuous soul, thou art come hither as full agent on behalf of thy father Santanu of immeasurable glory; be thou also the sole manager on my behalf in the matter of the bestowal of this my daughter. But, O amiable one, there is something else to be said, something else to be reflected upon by thee. O suppressor of foes, those that have daughters, from the very nature of their obligations, must say what I say. O thou that art devoted to truth, the promise thou hast given in the presence of these chiefs for the benefit of Satyavati, hath, indeed, been worthy of thee. O thou of mighty arms, I have not the least doubt of its ever being violated by thee. But I have my doubts in respect of the children thou mayst beget.' "Vaisampayana continued, 'O king, the son of Ganga, devoted to truth, having ascertained the scruples of the chief of the fishermen, then said, moved thereto by the desire of benefiting his father, 'Chief of fishermen, thou best of men, listen to what I say in the presence of these assembled kings. Ye kings, I have already relinquished my right to the throne, I shall now settle the matter of my children. O fisherman, from this day I adopt the vow of Brahmacharya (study and meditation in celibacy). If I die sonless, I shall yet attain to regions of perennial bliss in heaven!'