מדרש על משלי 12:18

(Fol. 22) (Pr. 12, 18) There is that speaketh like the piercing of a sword; but the tongue of the wise is health; i.e., whoever utters [a vow] deserves to be pierced with a sword, but the tongue of the wise is curing. We are taught that R. Nathan says: "Whoever makes a vow is like unto one who builds an idolatrous altar; whoever fulfills his vow is like unto one who offers sacrifices upon it."