What is the ruling on combining intentions in voluntary fasting, and does a Muslim receive the reward for all the combined intentions, and is there any detail regarding cases of combining intentions in voluntary fasting?

If the fasting of the White Days coincides with Mondays and Thursdays and also with the month of Muharram, and the fasting person intends to fast all of them, then it is hoped that he will receive the reward for fasting all of them.

If he fasts an obligatory fast on these days, he will also receive the reward of the supererogatory fast according to some jurists. The conclusion is that whoever fasts the days for which fasting is emphasized with the intention of an obligatory fast will receive the reward of both the obligatory fast and the supererogatory days, even if he does not receive the full, specific reward associated with what is sought.

Fasting on the aforementioned days (such as the Day of Arafah, Ashura, the White Days, and six days of Shawwal) is attributed to them, even if one intends something else by it.