Reference: https://twitter.com/osaimi0543/status/1393755567433342978
أفضل ما يُصام من أيَّام الأسبوع الاثنين ثمَّ الخميس، فمن تحرَّى صيام ستة شوالٍ فيهما اجتمع له فضيلتان، فإن وافق أحدهما أيَّام البيض اجتمع فيه مع الستِّ ثلاث فضائل، فمن نواها كلَّها عظُم أجره.
— صالح العُصَيمي (@Osaimi0543) May 16, 2021
Shaykh Saalih al-‘Usaymee said:
The best of the days of the week on which to fast is Monday and Thursday.
So whoever intends to fast the six [fasts] of Shawwaal during them, then for him two virtues are combined.
And if either of these two coincide with the full moon days (13th, 14th and 15th), then along with the six [fasts of Shawwaal] three virtues are combined [for him in total].
So whoever intends them all, then his reward increases.