Judges 12:5-6

The army of Gilead also posted guards at all the places where the soldiers from Ephraim could cross the Jordan River to return to their own land. Whenever one of the men from Ephraim would try to cross the river, the guards would say, “Are you from Ephraim?” “No,” the man would answer, “I'm not from Ephraim.” The guards would then tell them to say “Shibboleth,” because they knew that people of Ephraim could say “Sibboleth,” but not “Shibboleth.” If the man said “Sibboleth,” the guards would grab him and kill him right there. Altogether, 42,000 men from Ephraim were killed in the battle and at the Jordan.