What is the ruling on one who vowed to fast three days with their nights if he returned to masturbation, then became unable to fulfill his vow?

This vow is invalid and must not be fulfilled, because refraining from food and drink is self-torture that Allah does not approve of. And even if the intention behind the continuous fasting (wisal) was to draw closer to Allah, it is still disliked (makruh), and a vow of something disliked does not necessitate its fulfillment. Moreover, masturbation must be abandoned because it is forbidden in Islamic law.