In the Adi Parva of the Mahabharata, King Shantanu wants to marry Satyavati. Her father has doubts about the rights of her future sons. Shantanu’s son Devavrata answers him in front of the assembled chiefs: “Ye kings, I have already relinquished my right to the throne.”
The father still has doubts about Devavrata’s own children. So Devavrata adds: “O fisherman, from this day I adopt the vow of Brahmacharya,” lifelong celibacy. By this vow he became known as Bhishma.