The ruling on fulfilling a vow, and if one vows to fast on a Friday that is not isolated, but delays fulfilling it, what is required of him?

Question:
May Allah reward you. The questioner, identified as "Ayn M" from the southern region, says: I vowed to fast on Thursday and Friday. I fasted on Thursday but did not fast on Friday because fasting on that day alone is prohibited. My question is: Should I fast on Friday or on another day? Also, do I owe an expiation if I do not fast on Friday? Please rule for us, may Allah reward you with good.

Answer:
It is obligatory for you to fast on Friday if you have vowed to fast on it. There is no prohibition in this; rather, it is disliked to fast on Friday alone, according to the opinion of some scholars. However, if you fast it together with another day, such as fasting on Thursday before it or Saturday after it, the concern is removed. This applies to voluntary fasting. As for a vow, a vow is obligatory. The Messenger of Allah (peace and blessings be upon him) said: , . Therefore, it is obligatory for you to fast in place of the Friday you missed, and to pay the expiation for an oath for delaying the fasting you vowed for that day. Yes.