Judges 21:5
And the children of Israel said, Who is there among all the tribes of Israel that came not up with the congregation unto the Lord? For they had made a great oath concerning him that came not up to the Lord to Mizpeh, saying, He shall surely be put to death.
Cross-reference
In Judges 21:1, the oath about not giving daughters to Benjamin is recorded; here the people recall another oath about coming to Mizpah.
Judges 21:10 records the execution of the oath—smiting Jabesh-gilead for not coming to Mizpeh.
In Judges 21:18, the oath against giving wives to Benjamin is restated; both are oaths made by Israel at Mizpah.
In Judges 5:23, Meroz is cursed for not coming to help; here the same principle curses those who failed to assemble at Mizpah.
Judges 20:1 describes the assembly at Mizpeh where the oath was made, directly referenced in Judges 21:5.
Judges 20:8 shows the people's unified resolve after the assembly, providing context for the oath's seriousness.
In 1 Samuel 11:7, Saul threatens punishment for those who don't join the battle; here the oath threatens death for not coming to Mizpah.