Is it permissible to fast the three White Days if they fall on Friday, Saturday, and Sunday, or Thursday, Friday, and Saturday, or Wednesday, Thursday, and Friday?

The prohibition against fasting on specific days is due to singling them out. However, if such a day coincides with a habitual fast, then there is no harm in fasting it. This is based on the Prophet's (peace be upon him) saying: "Do not single out Friday for fasting among other days unless it coincides with a day one of you habitually fasts," and his saying: "Do not precede Ramadan with a fast of one or two days, except for a man who habitually fasts, let him fast it." Accordingly, there is no objection to fasting the White Days if they coincide with some of those specific days.