Question: Is it permissible to give voluntary charity (sadaqa) while one has debts of unpaid zakat, to observe a voluntary (nafila) fast while one has missed fasts from Ramadan, or to do any other voluntary act of worship while one has debts of an obligatory act of worship of the same kind?
ANSWER
It is not permissible because fard acts of worship are of utmost importance. It is stated in hadith-i sharifs:

(The best jihad is to do fard [obligatory] acts of worship.) [Imam-i Ahmad]

(While everybody is busy doing voluntary acts of worship, strive to do fard ones.) [Miftah-un-Najat]

(One cannot approach Allah through anything as close as one approaches Him through fard acts of worship.) [Bayhaqi]

(The voluntary acts of worship of a person who has salats to make up will not be accepted.) [Durrat-ul-Fakhira]

(On the Day of Judgment, people will be questioned about salat first. If one's salats are found correct, one will be saved. If they are not correct, one will be miserable.) [Hakim]

Hadrat Abu Bakr said the following in his will to Hadrat 'Umar:

"If you carry out in the daytime the rights of Allah that you must do at night or if you carry out at night the rights of Allah that you must do in the daytime, He will not accept them. He will not accept your voluntary acts of worship unless you do those acts of worship that are fard on you" (Kitab-ul-Haraj).

Hadrat Imam-i Rabbani stated:

"The value of voluntary acts of worship compared with obligatory ones is not even like that of a drop of water compared with an ocean" (260th Letter).

"If a voluntary act of worship causes one to skip a fard act of worship, then it is not counted as an act of worship, but, in fact, it is harmful" (123rd Letter).

Therefore, if one has a debt of zakat worth a dollar and if one, before paying one's debt, provides money for the building of a million mosques or gave billions of money to millions of people for charity, none of them would be acceptable.

If one skips a fast of Ramadan without any justification and instead of it if one observes voluntary fasts for the remainder of one's life, they will not be accepted. Moreover, if one who has missed a fast of Ramadan makes it up after Ramadan and then observes a fast every day, one will not earn the reward (thawab) given in return for a fast observed in Ramadan. Making it up only acquits one of the debt; one cannot earn the reward of a fast observed in Ramadan because our Master the Prophet stated:

(If a person does not fast for a single day in Ramadan, he cannot earn the thawab of this single day, even if he fasts all the year round instead of it.) [Tirmidhi]

Sayyid Abd al-Qadir Ghaylani stated:

(If a person has a missed fard salat, his performing voluntary salat is like [the case of] a pregnant woman who has a miscarriage when she is about to give birth to the baby. The woman cannot be said to be pregnant, nor can she be called a mother anymore. So is this person. Unless he makes up his missed salats, Allahu ta’ala will not accept his voluntary salats.) This hadith-i sharif shows that it is idiocy to spend time performing nafila salats while one has salats to make up. A person performing nafila salats while he/she has debts of omitted salats is like a debtor taking a present to the person to whom he/she owes, which, normally, is not acceptable. A Believer is like a business person. The fard salats are his/her capital, and voluntary salats are his/her profit. Unless the capital is rescued, they will give no profit. (Futuh al-Ghayb)

"Perform a two-rak'at salat before going on a journey. If you have salats to make up, then you must make up two or three salats because it is idiocy to perform voluntary salats when one has salats to make up" (The pamphlet Bay wa Shir'a).

Hadrat Sayyid Abdulhakim Arwasi, who was an expert on the fiqh of the four madhhabs, said:
"One who has years of missed salats must perform sunnat salats with the intention of making up missed salats. Performing sunnat salats by intending in this way is necessary in all of the four madhhabs."

That it is necessary to add the intention of a qada salat when intending to perform a sunnat salat is written in the fatwa of Ramiz-ul-Mulk, the superintendent of fatwa in Tripoli, which is written in the periodical named Ash-Shihab.

It is written in the book Tatarhaniyya, "When performing a sunnat salat, it is better to make a secondary intention of a qada salat as well." (Uyun-ul-Basair, p. 103)

If one performs sunnat salats with the intention of qada salats, one's sunnat salats will be accepted, too. (Fatawa-i Kubra)