Deuteronomy 23:21

19 Thou shalt not lend upon usury to thy brother; usury of money, usury of victuals, usury of any thing that is lent upon usury:

20 Unto a stranger thou mayest lend upon usury; but unto thy brother thou shalt not lend upon usury: that the LORD thy God may bless thee in all that thou settest thine hand to in the land whither thou goest to possess it.

When thou shalt vow a vow unto the LORD thy God, thou shalt not slack to pay it: for the LORD thy God will surely require it of thee; and it would be sin in thee.

22 But if thou shalt forbear to vow, it shall be no sin in thee.

23 That which is gone out of thy lips thou shalt keep and perform; even a freewill offering, according as thou hast vowed unto the LORD thy God, which thou hast promised with thy mouth.

Do read the surrounding verses too, because the context often says more than a single verse.

Compare

BSB
If you make a vow to the LORD your God, do not be slow to keep it, because He will surely require it of you, and you will be guilty of sin.
KJV
When thou shalt vow a vow unto the LORD thy God, thou shalt not slack to pay it: for the LORD thy God will surely require it of thee; and it would be sin in thee.
WEB
When you vow a vow to the LORD your God, you shall not be slack to pay it, for the LORD your God will surely require it of you; and it would be sin in you.
ASV
When thou shalt vow a vow unto Jehovah thy God, thou shalt not be slack to pay it: for Jehovah thy God will surely require it of thee; and it would be sin in thee.
DARBY
When thou vowest a vow to Jehovah thy God, thou shalt not delay to perform it; for Jehovah thy God will certainly require it of thee, and it shall be sin in thee.
BLB
When you make a vow to YHWH your God, you shall not delay to pay it. For YHWH your God will surely require it of you, and it would be sin in you.
ÅB
Når du gjør Herren din Gud et løfte, da skal du ikke vente med å holde det; for Herren din Gud vil kreve det av deg, og du vil få synd på deg.
OTB
Hvis du gir et løfte til Herren din Gud, må du ikke nøle med å oppfylle det, for Herren din Gud vil sikkert kreve det av deg, og du vil være skyldig i synd.
B1930
Når du gjør Herren din Gud et løfte, da skal du ikke vente med å holde det; for Herren din Gud vil kreve det av dig, og du vil få synd på dig.

Study notes (Tyndale)

Original text and word study

Cross references