Ambrose of Milan, on Judg 11:39

“And the two months being expired, she returned to her father, and he did to her as he had vowed, and she knew no man. From thence came a fashion in Israel, and a custom has been kept:”

“It is also sometimes contrary to duty to fulfill a promise or to keep an oath. As was the case with Herod, who swore that whatever was asked he would give to the daughter of Herodias, and so allowed the death of John, that he might not break his word. And what shall I say of Jephthah, who offered up his daughter in sacrifice, she having been the first to meet him as he returned home victorious; whereby he fulfilled the vow which he had made that he would offer to God whatever should meet him first. It would have been better to make no promise at all than to fulfill it in the death of his daughter.”

Imported from an open dataset — not yet checked against the printed edition.