No, Sunnah prayers are highly recommended. And Nafl prayers are recommended and added benefit.
On the day of judgement, 1st action counted will be 5 daily prayers, if they are lacking in count or perfection, the Allah will ask to see if My servant has supplementary prayers to make up the weight in positive for a person. Also I have experienced that when I pray supplementary prayers, I feel closer to Allah and I improve my perfection in prayers.
I'm sure there are other rewards, but this is what I can think of right now.
The linguistic meaning of QADA is compensation.
Revelation, quran and Sahih hadith speak of compensation for a single obligatory prayer or a few obligatory prayers which have been missed due to unavoidable circumstances.
Since witr and sunnah of fajr do not fall under obligatory prayers they cannot be compensated. They cannot be made up if you have missed them unintentionally.
Secondly, the reward system of Allah is so beautiful that if a person prays 28 sunnah of fajr in a month and missed sunnah on a random day because of sleep or unconsciousness, Allah willing his reward is written as if he has prayed the sunnah.
In Islam, sunnah, also spelled sunna (Arabic: سنة), are the traditions and practices of the Islamic prophet Muhammad that constitute a model for Muslims to follow. The sunnah is what all the Muslims of Muhammad's time evidently saw and followed and passed on to the next generations.[1] According to classical Islamic theories,[2] the sunnah are…
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