Responding to an invitation for one who is fasting a voluntary fast

Question:
The Shaykh is not someone who habitually fasts on Thursdays. So if he is invited to an occasion, does he respond to the invitation and break his fast, or does he decline the invitation and continue fasting, even though the fast is a voluntary fast?

Answer:
He has the choice. He has the choice: if he wishes, he goes, and if he wishes, he does not go. And if he goes, he also has the choice: if he wishes, he eats and breaks the fast, because the fast is voluntary, and it is permissible to break a voluntary fast. The only thing whose breaking is forbidden is the obligatory fast, whether for its performance or making it up. As for the voluntary fast, it is permissible to break it. So if he goes, he has the choice: if he wishes, he breaks the fast and eats, and if he wishes, he invites them and leaves in order to please them. He attends to please them, makes du'a for them, and leaves, remaining in his fast. He has the choice in this. The best for him, if they are affected by his absence, is that he attends on a day when he does not eat. Otherwise, he makes du'a for them and informs them that he is fasting, and makes du'a for them. Yes.