Judges 12:3-6
12:3 When I saw that you were not going to help, I risked my life and advanced against the Ammonites, and the Lord handed them over to me. Why have you come up to fight with me today?”
12:4 Jephthah assembled all the men of Gilead and they fought with Ephraim. The men of Gilead defeated Ephraim, because the Ephraimites insulted them, saying, “You Gileadites are refugees in Ephraim, living within Ephraim’s and Manasseh’s territory.”
12:5 The Gileadites captured the fords of the Jordan River opposite Ephraim. Whenever an Ephraimite fugitive said, “Let me cross over,” the men of Gilead asked him, “Are you an Ephraimite?” If he said, “No,”
12:6 then they said to him, “Say ‘Shibboleth!’” If he said, “Sibboleth” (and could not pronounce the word correctly), they grabbed him and executed him right there at the fords of the Jordan. On that day forty-two thousand Ephraimites fell dead.