Whenever a man makes a vow to Adonai or swears an oath to obligate himself by a pledge, he is not to violate his word but do everything coming out of his mouth.
“Or if a person swears rashly with his lips to do evil or to do good—about anything that one might utter rashly by an oath, though it is hidden from him, when he realizes it, then he will be guilty of one of these.
But do not give in to them, for more than forty of them have bound themselves by an oath not to eat or drink until they have killed him. Even now, they are ready and waiting for your consent.”
Then Jephthah went with the elders of Gilead, and the people made him head and chief over them, after Jephthah repeated all his terms before Adonai at Mizpah.
Then at the end of two months she returned to her father, who did with her according to his vow he had made—so she was never intimate with a man. So it became a custom in Israel,