Question: What is a nafila (voluntary) salat? Are the sunnat salats of the five daily salats, too, considered nafila salats?
ANSWER
Nafila salats are those salats that are neither fard nor wajib. The sunnat salats of the five fard salats and other non-wajib salats are all nafila salats. All sunnat salats, muakkadah or non-muakkadah, are nafila. Some pertinent hadith-i sharifs are as follows:

(A person who performs 12-rak'at nafila salat, that is, 4 rak'ats before Salat az-Zuhr, 2 rak'ats after Salat az-Zuhr, 2 rak'ats after Salat al-Maghrib and Salat al-Isha, 2 rak'ats before Salat al-Fajr, will enter Paradise.) [Nasai]

(Whoever keeps performing a 4-rak'at nafila salat before and after Salat az-Zuhr, Hell will be forbidden to him.) [Tirmidhi]

Hadrat Aisha, our blessed mother, said, "The Messenger of Allah did not use to perform nafila salats on a regular basis, except the 2-rak'at nafila salat of Salat al-Fajr" (Bukhari).

It is written in all fiqh books that sunnat salats are under the umbrella term nafila salats. Some excerpts from fiqh books are as follows:

1. "Nafila acts of worship are those acts of worship that are neither fard nor wajib. All sunnat acts of worship are termed nafila" (Tahtawi).

2. "Nafila salats are divided into two: rawatib and raghaib. Rawatib are those sunnat salats performed before and after fard salats. Raghaib are other nafila salats, such as Salat ad-Duha, Salat al-Awwabin, and Salat at-Tahajjud. The reason why sunnat acts of worship are termed nafila is that the word nafila is more comprehensive. Every sunnat is nafila, but not every nafila is sunnat" (Ni'mat-i Islam).

3. "When nafila and rawatib sunnat salats are performed with the intention of salat only or with the intention of any kind of salat other than sunnat salats, they will be valid" (Ashbah).

As is seen, any salat [e.g., a qada salat] performed in addition to the current fard salat within the time of it is considered the sunnat salat of that fard salat. For this reason, if one, before starting to perform a sunnat salat, intends simultaneously both to perform the sunnat salat and to perform a qada salat, one will not be considered to have omitted the sunnat salat.

4. "A sunnat performed with the intention of salat only is valid because the sunnat salats of the five fard salats means the salats
performed by our Master the Prophet. It was afterwards that those salats were named sunnats. When performing the sunnats of the five daily salats, the Messenger of Allah used to intend, 'I intend to perform salat for Allah’s sake.' He did not intend, ‘I intend to perform the sunnat.’ Any salat performed so in every salat time becomes the salat that is called sunnat" (Radd-ul-Mukhtar, Uyun-ul-Basair, Halabi).

5. "As it is written in the book Tajnis, the sunnat salats of the five daily salats are considered nafila, so they can be performed with the intention of a nafila salat" (Radd-ul-Mukhtar).

6. "The sunnat salats of the five daily salats and Salat at-Tarawih are in the category of nafila salats. When making intention for them, it suffices to say, 'I intend to perform salat'" (Durr-ul-Mukhtar, Durar).

7. "The sunnat salats of the five daily salats and other non-wajib salats are nafila. All sunnat salats, muakkadah or non-muakkadah, are nafila" (Durr-ul-Mukhtar, Radd-ul-Mukhtar, Halabi).

8. "Every sunnat salat is nafila, but not every nafila salat is sunnat" (Radd-ul-Mulhtar, Ni'mat-i Islam).

9. "It is permissible to perform the sunnat salats of the five daily salats by sitting even if there is no excuse to do so" (Jawhara, Hidaya).

10. "Nafila salats include sunnat salats as well. Qadi Imam-i Abu Zayd stated, "Performing nafila salats was commanded so that they may compensate for the deficiencies in one's obligatory salats. If one is able to perform fard salats perfectly, no objection is raised to one if one does not perform sunnat salats" (Durar).

11. "Nafila salats of a person who has salats to make up will not be acceptable. Sunnat salats, too, are considered nafila" (An-Nawadir-ul-Fiqhiyya fi Madhhab-il-Aimmat-il Hanafiyya).

12. "When one performs qada salats instead of sunnat salats, one will also earn the reward of performing sunnat salats" (Maktubat-i Masumiyya, Vol. 2, Letter 63).

13. "In the other three madhhabs, sunnat salats are in the category of nafila salats, just as it is the case in the Hanafi Madhhab" (Al-Fiqh 'Ala Al-Madhaahib al-Arba'ah).

14. "Voluntary acts of worship are of no value when compared with obligatory ones. They are not even a drop of water compared with an ocean. 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" (Maktubat-i Rabbani, Vol. 1, Letter 260).

15. "Raghaib and rawatib salats cannot reach fard salats in reward and superiority. No nafila act of worship can acquit a person of a fard obligation. It has no place in Islam, unlike what the layman says, to claim that doing nafila acts of worship will substitute for obligatory acts of worship, such as claiming that performing Salat al-Awwabin will compensate for one's omitted salats" (Ruh-ul-Bayan, Vol. 3, p. 127).

16. It is stated in a hadith-i sharif related from Hadrat Ali:
(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 her 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.) [Zahira-i Fiqh, Futuh-ul-Ghayb] Abdulhaqq-i Dahlawi, a scholar of the Hanafi Madhhab, explains this hadith as follows, "This hadith-i sharif indicates that the sunnat salats of those who have salats omitted will not be accepted because sunnat salats, too, are nafila."