Jephthah vowed to God that if He would help him win the battle then Jephthah would sacrifice the first thing that came from his house to greet him. His daughter was the first to greet him, so he sacrificed her. It is found in Judges chapter 11.
See above answer. To be honest I didn't know that one but its a history event rather then needed for day to day or helping get through things and so I think I'm fine not knowing that one although it is pretty cool sounding.