נָדַר

And she made a vow, pleading, “O LORD of Hosts, if only You will look upon the affliction of Your maidservant and remember me, not forgetting Your maidservant but giving her a son, then I will dedicate him to the LORD all the days of his life, and no razor shall ever come over his head.”

then the LORD your God will choose a dwelling for His Name. And there you are to bring everything I command you: your burnt offerings and sacrifices, your tithes and special gifts, and all the choice offerings you vow to the LORD.

I am the God of Bethel, where you anointed the pillar and made a solemn vow to Me. Now get up and leave this land at once, and return to your native land.’”

After two months, she returned to her father, and he did to her as he had vowed. And she had never had relations with a man.So it has become a custom in Israel

But if the one making the vow is too poor to pay the valuation, he is to present the person before the priest, who shall set the value according to what the one making the vow can afford.