Judges 11:31
Then it shall be, that whatsoever cometh forth of the doors of my house to meet me, when I return in peace from the children of Ammon, shall surely be the LORD’s, and I will offer it up for a burnt offering. Then it shall be, that whatsoever cometh forth of the doors of my house to meet me, when I return in peace from the children of Ammon, shall surely be the LORD’s, and I will offer it up for a burnt offering.
The vow in the verse was made by Jephthah when God raised him up to deliver Israel from the Ammonites. That deliverance came after Israel had suffered under Ammonite oppression for eighteen years. The account containing the verse shows that Israel soon forgot the lesson taught by that suffering.