As for the Days of Tashrīq, an explicit prohibition was reported against fasting them, for they are festival days—days of eating, drinking, and remembering Allah. Hence, fasting on them is unlawful, except for the pilgrim who cannot afford the sacrificial animal required for the rites of tamattuʿ or qirān. A pilgrim performing qirān or tamattuʿ must offer a hady (sacrificial animal); if he cannot obtain one, he is to fast three days during the Hajj even should those days coincide with the Days of Tashrīq. In the ḥadīth of ʿĀʾishah, the Prophet ﷺ “forbade fasting the Days of Tashrīq except for someone who is making up for a sacrifice owed for tamattuʿ or qirān.”

This ruling is confined to that particular case. Outside the Days of Tashrīq, the preferable option is to fast the white days.

Question: Is it true that the Messenger never left off fasting the white days whether travelling or resident, or is it merely a recommended fast?

Answer: The Messenger ﷺ used to fast voluntarily and did so frequently. He would fast to such an extent that people would say, “He never breaks his fast,” and at other times he would refrain from fasting until they would say, “He does not fast.” In short, he engaged in many supererogatory fasts both at home and while travelling. As for his unfailingly observing the white days in particular, I do not know; nothing on that point comes to mind at present.