Judges 11:29-40 New Revised Standard Version (NRSV)
29 Then the spirit of the Lord came upon Jephthah, and he passed through Gilead and Manasseh. He passed on to Mizpah of Gilead, and from Mizpah of Gilead he passed on to the Ammonites. 30 And Jephthah made a vow to the Lord, and said, “If you will give the Ammonites into my hand, 31 then whoever comes out of the doors of my house to meet me, when I return victorious from the Ammonites, shall be the Lord’s, to be offered up by me as a burnt offering.” 32 So Jephthah crossed over to the Ammonites to fight against them; and the Lord gave them into his hand. 33 He inflicted a massive defeat on them from Aroer to the neighborhood of Minnith, twenty towns, and as far as Abel-keramim. So the Ammonites were subdued before the people of Israel.
34 Then Jephthah came to his home at Mizpah; and there was his daughter coming out to meet him with timbrels and with dancing. She was his only child; he had no son or daughter except her. 35 When he saw her, he tore his clothes, and said, “Alas, my daughter! You have brought me very low; you have become the cause of great trouble to me. For I have opened my mouth to the Lord, and I cannot take back my vow.” 36 She said to him, “My father, if you have opened your mouth to the Lord, do to me according to what has gone out of your mouth, now that the Lord has given you vengeance against your enemies, the Ammonites.” 37 And she said to her father, “Let this thing be done for me: Grant me two months, so that I may go and wander[a] on the mountains, and bewail my virginity, my companions and I.” 38 “Go,” he said and sent her away for two months. So she departed, she and her companions, and bewailed her virginity on the mountains. 39 At the end of two months, she returned to her father, who did with her according to the vow he had made. She had never slept with a man. So there arose an Israelite custom that 40 for four days every year the daughters of Israel would go out to lament the daughter of Jephthah the Gileadite.