Judges 11:39-40

Modern English Version

³⁹ At the end of two months she returned to her father, and he did to her according to the vow that he had made. She had not ever slept with a man.

So it became a custom in Israel ⁴⁰ that the women of Israel would commemorate the daughter of Jephthah the Gileadite for four days each year.