Recanting Oaths
You mean to make a vow to do a prohibited act? It is obligatory to break such a vow and pay the atonement. If you mean to vow not to do a prohibited act, of course one is not supposed to break it. If one breaks it and commit the prohibited act, one is guilty of two sins, breaking of vow and commiting the prohibit s act. One should repent and also pay the atonement.
What I mean is recantig vows, which involve a prohibited act,