Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
You can either combine two intentions of fasting or fast each kind separately.
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
You may do this according to the rulings of the Shafi`i School of fiqh; for, they say, it is permissible to combine both in one intention and thus reaping the rewards of both.
It is not different from someone entering the mosque, for instance, before Zhuhr prayer before the congregational prayer begins and offering two rak`ahs of sunnah. By doing so, he stands to gain rewards for the sunnah before Zhuhr as well as that of tahiyyat al-masjid (greeting the mosque).
Having said this, I should also point out that the above view is not shared by other juristic schools. They do not allow for anyone to combine the niyyah of qada’ (making up) for missed fasts of Ramadan with the nafl (optional) fasts of Shawwal.
They insist that one needs to have two separate niyyahs. So, according to this view, one should make up for the fasts missed first, and then independently formulate another niyyah to fast the six days of Shawwal. One may also fast the sunnah fasts of Shawwal and later make up for the fasts he or she has missed.
It is up to you to choose one of the above views. Although no one can deny that one may stand to gain greater rewards in doing them separately, there is no need to be rigid on this issue, for doing so is akin to limiting Allah’s mercy, which is undoubtedly limitless.
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.
Source: Excerpted, with slight modification from www.askthescholar.com