Deuteronomy 23:22

Overview - Deuteronomy 23
1	Who may or may not enter into the congregation.
9	Uncleanness is to be avoided in the host.
15	Of the fugitive servant.
17	Of filthiness.
18	Of abominable sacrifices.
19	Of usury.
21	Of vows.
24	Of trespasses.

Deuteronomy 23:22  (King James Version)
But if thou shalt forbear to vow, it shall be no sin in thee.