What is the ruling on saying "I am fasting the Six White Days"? And should one say "the Six of Shawwal" or "the Six White Days"? And what is the origin of the appellation "the Six White Days"? And was this appellation in existence during the time of the Messenger and the Companions?

The White Days are the thirteenth, fourteenth, and fifteenth of every Hijri month. They are called that because their nights are illuminated by the moon, and it is recommended to fast them. As for fasting the six days of Shawwal, it is also recommended, but they are not called the White Six, and there is no basis for this appellation.