Judges 11:29-12:7 (NIV)
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. And Jephthah made a vow to the Lord: “If you give the Ammonites into my hands, 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.”
Then Jephthah went over to fight the Ammonites, and the Lord gave them into his hands. He devastated twenty towns from Aroer to the vicinity of Minnith, as far as Abel Keramim. Thus Israel subdued Ammon.
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. 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.”
“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. 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.”
“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. 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 that each year the young women of Israel go out for four days to commemorate the daughter of Jephthah the Gileadite.
The Ephraimite forces were called out, and they crossed over to Zaphon. They said to Jephthah, “Why did you go to fight the Ammonites without calling us to go with you? We’re going to burn down your house over your head.”
Jephthah answered, “I and my people were engaged in a great struggle with the Ammonites, and although I called, you didn’t save me out of their hands. When I saw that you wouldn’t help, I took my life in my hands and crossed over to fight the Ammonites, and the Lord gave me the victory over them. Now why have you come up today to fight me?”
Jephthah then called together the men of Gilead and fought against Ephraim. The Gileadites struck them down because the Ephraimites had said, “You Gileadites are renegades from Ephraim and Manasseh.” The Gileadites captured the fords of the Jordan leading to Ephraim, and whenever a survivor of Ephraim said, “Let me cross over,” the men of Gilead asked him, “Are you an Ephraimite?” If he replied, “No,” they said, “All right, say ‘Shibboleth.’” If he said, “Sibboleth,” because he could not pronounce the word correctly, they seized him and killed him at the fords of the Jordan. Forty-two thousand Ephraimites were killed at that time.
Jephthah led Israel six years. Then Jephthah the Gileadite died and was buried in a town in Gilead.