Deuteronomy 23:21

Thou shalt not slack to pay it, to wit, if the matter of it be lawful, and in thy own power. See Numbers 30:2. Not slack or delay, because delays may make thee both unable to pay it, and unwilling too, the sense of one's obligation growing every day weaker than other, &c. It would be sin in thee, i.e. it would be laid to thy charge as a sin, and bring judgment upon thee.