Yes , it is permissible.

Can we have two niyyah, fasting mondays and thursdays and fasting 6 days of the month of shawwal? Therefore, everytime we fast mondays and thursdays, they can be counted for two days of fasting the month of shawwal until we finish fasting the 6 days of the month of shawwal?

Fasting | June 29, 2017 4:14 am
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If a muslimah didn’t fast the obligatory fasts frm young age for alot of reasons, now she wants to recover n she calculated, its more than 500dys, wants to fast but she diagnosed with type 2 diabetes, the Dr told do not fast so need ur kind help, what is Islamic rule?
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During Ramadan a brother missed Zuhr and Asr prayers only for 3days consecutively, how does he makeup and is his Ramadan for those three days valid.