Is it permissible for me to fast the six days of Shawwaal with the same intention as making up the days I did not fast in Ramadaan because of menstruation?.
Praise be to Allaah. That is not valid, because fasting the six days of Shawwaal can only be done after fasting Ramadaan in full.
Shaykh Ibn ‘Uthaymeen said in Fataawa al-Siyaam (438):
Whoever fasts the day of ‘Arafah, or the day of ‘Ashoora’, but still owes days from Ramadaan, his fast is valid, but if he intends to fast this day to make up for a missed Ramadaan fast, he will have two rewards: the reward for the day of ‘Arafah or ‘Ashoora’ along with the reward for making up the missed fast. This has to do with voluntary fasts in general that are not connected to Ramadaan. With regard to fasting the six days of Shawwaal, they are connected to Ramadaan and can only done after making up missed Ramadaan fasts. If he fasts them before making up missed Ramadaan fasts he will not attain that reward, because the Prophet (peace and blessings of Allaah be upon him) said: “Whoever fasts Ramadaan then follows it with six days of Shawwaal, it will be as if he fasted for a lifetime.” It is well known that whoever still owes days from Ramadaan is not regarded as having fasted Ramadaan until he makes up the days he missed.
Is it permissible to fast the six days of Shawwaal every Monday and Thursday with both intentions of fasting the six days of Shawwaal and fasting on Mondays and Thursdays to attain both rewards? What is the rule on combining more than one intention in one deed? For example, is it permissible to fast in Ramadhaan and on Mondays intend the fast of Ramadhaan along with the Sunnah of fasting on Mondays?
All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad , is His slave and messenger.
Combining more than one intention in a single deed is what is known among the people of knowledge as “At-Tashreek”. Its ruling is that if it is done in terms of means or in intersecting matters, it is valid and the required purpose of both acts of worship is achieved. For example, if someone performs Ghusl due to Janaabah on Friday for the sake of Friday and for the sake of eliminating his Janaabah, then his Janaabah is eliminated and he attains the reward of having a bath on Friday. If one of the two acts of worship is not intended but the other is intended for itself, it is valid to combine them and this does not detract from the act of worship like performing the prayer of greeting the Masjid with an obligatory or some other Sunnah prayer. Greeting the Masjid is not intended for itself but what is intended is occupying the place with prayer and this happened.
If this is established, then know that there is no harm in combining between fasting on Mondays and Thursdays and any other fasting. Fasting on Mondays and Thursdays is recommended because they are the days when deeds are presented to Allaah The Almighty. The Prophet , liked fasting them for his deeds to be raised while he is fasting. The Prophet , said: “Deeds are presented (to Allaah) on Monday and Thursday and I like my deeds to be presented when I am fasting.” [As-Suyooti on the authority of Abu Hurayrah ; Al-Albaani: Saheeh]
The questioner should not combine the intention of obligatory fasting with any voluntary fasting. The intended meaning of fasting on Mondays and Thursdays is achieved without the need of an intention.
Allaah Knows best.