Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.   Wa alaikum assalam wa rahmatullahi wa barakatuh.   As to what follows:   In response to your question, we say:     What is the ruling of combining the intention of fasting the six days of Shawwal with fasting the days of the full moon? There is no problem in combining more than one intention in one fast if it is a Sunnah fasting. Thus a person may make the intention to fast a day from the six days of Shawwal, and also intend to fast the three days that are fasted voluntarily every month. If his fasting coincides with the days of the full moon he can also make an intention to fast them. Similarly, if his fasting coincides with Monday, he can also make an intention to fast on Monday because his intention can suffice for that. However, combining the intention of fasting between a compulsory and an optional fast is not valid because these are two different fasts, they are not one type because one is compulsory and the other is optional.