A muʿtakif must fast during the days of iʿtikāf. Therefore, iʿtikāf performed by someone who cannot [legally] fast [during those days] – such as a traveller who does not intend to stay somewhere for ten days, a sick person, a woman in menstruation (i.e. a ḥāʾiḍ), and a woman who is experiencing lochia (nifās) – is not correct.
Furthermore, on the days of iʿtikāf, it is not necessary to fast especially for performing iʿtikāf; rather, it is acceptable for one to keep any fast during iʿtikāf, even a fast that one has been hired to keep (istījārī), or a recommended fast, or a lapsed (qaḍāʾ) fast.