Fulfilling Oaths and Vows According to Maimonides

(xii) Maimonides, Laws of Vows 1:4:
“It is a positive commandment of Scriptural origin for a person to fulfill his oath or vow, whether it be a vow involving prohibitions or a vow of sanctification, as it is stated (-Deuteronomy 23:24), ‘that which your lips give out (utter) heed, and do as you have promised.’ And it is stated (-Numbers 30:3), ‘As all that he gives out from his mouth (utters) he shall do.’"