Judges 11:29-40 Good News Translation (GNT)
29 Then the spirit of the Lord came upon Jephthah. He went through Gilead and Manasseh and returned to Mizpah in Gilead and went on to Ammon. 30 Jephthah promised the Lord: “If you will give me victory over the Ammonites, 31 I will burn as an offering the first person that comes out of my house to meet me, when I come back from the victory. I will offer that person to you as a sacrifice.”
32 So Jephthah crossed the river to fight the Ammonites, and the Lord gave him victory. 33 He struck at them from Aroer to the area around Minnith, twenty cities in all, and as far as Abel Keramim. There was a great slaughter, and the Ammonites were defeated by Israel.
34 When Jephthah went back home to Mizpah, there was his daughter coming out to meet him, dancing and playing the tambourine. She was his only child. 35 When he saw her, he tore his clothes in sorrow and said, “Oh, my daughter! You are breaking my heart! Why must it be you that causes me pain? I have made a solemn promise to the Lord, and I cannot take it back!”
36 She told him, “If you have made a promise to the Lord, do what you said you would do to me, since the Lord has given you revenge on your enemies, the Ammonites.” 37 But she asked her father, “Do this one thing for me. Leave me alone for two months, so that I can go with my friends to wander in the mountains and grieve that I must die a virgin.” 38 He told her to go and sent her away for two months. She and her friends went up into the mountains and grieved because she was going to die unmarried and childless. 39 After two months she came back to her father. He did what he had promised the Lord, and she died still a virgin.
This was the origin of the custom in Israel 40 that the Israelite women would go out for four days every year to grieve for the daughter of Jephthah of Gilead.
Judges 11:29-40 New International Version (NIV)
29 Then the Spirit of the Lord came on Jephthah. He crossed Gilead and Manasseh, passed through Mizpah of Gilead, and from there he advanced against the Ammonites. 30 And Jephthah made a vow to the Lord: “If you give the Ammonites into my hands, 31 whatever comes out of the door of my house to meet me when I return in triumph from the Ammonites will be the Lord’s, and I will sacrifice it as a burnt offering.”
32 Then Jephthah went over to fight the Ammonites, and the Lord gave them into his hands. 33 He devastated twenty towns from Aroer to the vicinity of Minnith, as far as Abel Keramim. Thus Israel subdued Ammon.
34 When Jephthah returned to his home in Mizpah, who should come out to meet him but his daughter, dancing to the sound of timbrels! She was an only child. Except for her he had neither son nor daughter. 35 When he saw her, he tore his clothes and cried, “Oh no, my daughter! You have brought me down and I am devastated. I have made a vow to the Lord that I cannot break.”
36 “My father,” she replied, “you have given your word to the Lord. Do to me just as you promised, now that the Lord has avenged you of your enemies, the Ammonites. 37 But grant me this one request,” she said. “Give me two months to roam the hills and weep with my friends, because I will never marry.”
38 “You may go,” he said. And he let her go for two months. She and her friends went into the hills and wept because she would never marry. 39 After the two months, she returned to her father, and he did to her as he had vowed. And she was a virgin.
From this comes the Israelite tradition 40 that each year the young women of Israel go out for four days to commemorate the daughter of Jephthah the Gileadite.