Wife asking husband’s permission to fast when he has another wife
Is it obligatory for a wife to ask her husband’s permission to fast if that is on the other wife’s day?
Answer
Praise be to Allaah.
If the husband is present with her then she should not fast without his permission, because he may need her. But if he is with his other wife and it is the other wife’s day, then it seems that it is o.k. for her to fast with or without his permission.
Shaykh Muhammad Saalih al-‘Uthaymeen, Majallat al-Da’wah, issue no. 1823, p. 54.