פירוש על בבא בתרא 147:11

"And now that I have sworn who will annul it for me?" This is surprising why can't Ha-shem annul it himself? Since we concluded in the tractate of Holiday Offerings (page 10A) that oaths can be annuled from the pasuk "that I swore in my anger" (psalms 95:11) the Gemarah explains that one can annul it for oneself. "Since I swore in my anger, I can nullify the vow (ibid.)." We see from here that one can annul one's own vows. However, this doesn't make sense because it says "One can't go back on one's word." (Numbers 30:3) We learn from here that even a scholar can't go back on his own vow (tractate of Promises page 21B). It says in chapter four of the tractate of Promises (page 23A) that there was a launderer who dissolved his vow, but this doesn't mean that he dissolved it himself. Rather that he found a way for its dissolution that was then carried out by the Rabbinic authorities.