Judges 11:30-40 Complete Jewish Bible (CJB)
30 Yiftach made a vow to Adonai: “If you will hand the people of ‘Amon over to me, 31 then whatever comes out the doors of my house to meet me when I return in peace from the people of ‘Amon will belong to Adonai; I will sacrifice it as a burnt offering.” 32 So Yiftach crossed over to fight the people of ‘Amon, and Adonai handed them over to him. 33 He killed them from ‘Aro‘er until you reach Minnit, twenty cities, all the way to Avel-K’ramim; it was a massacre. So the people of ‘Amon were defeated before the people of Isra’el.
34 As Yiftach was returning to his house in Mitzpah, his daughter came dancing out to meet him with tambourines. She was his only child; he had no other son or daughter. 35 When he saw her, he tore his clothes and said, “Oh, no, my daughter! You’re breaking my heart! Why must you be the cause of such pain to me? I made a vow to Adonai, and I can’t go back on my word.” 36 She said to him, “Father, you made a vow to Adonai; so do whatever you said you would do to me; because Adonai did take vengeance on your enemies the people of ‘Amon.” 37 Then she said to her father, “Just do this one thing for me — let me be alone for two months. I’ll go away into the mountains with my friends and mourn, because I will die without getting married.” 38 “You may go,” he answered, and he sent her away for two months. She left, she and her friends, and mourned in the mountains that she would die unmarried. 39 After two months she returned to her father, and he did with her what he had vowed; she had remained a virgin. So it became a law in Isra’el 40 that the women of Isra’el would go every year for four days to lament the daughter of Yiftach from Gil‘ad.
Judges 11:30-40 New International Version (NIV)
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.