Farz Prayers are those prayers that have been made obligatory upon the Muslims. There are 17 rakats of obligatory prayers in a day.

As for the wisdom in legislating these sunna prayers, Imam al-Haskafi mentions in al-Durr al-Mukhtar,

“The sunna prayers after the obligatory prayers were legislated to make up for the deficiency in the obligatory prayer, and the sunna prayers before the obligatory prayers are to cut the Devil from his greed.”

Sunna Prayers make up for deficiencies within the obligatory prayers themselves, caused by missing some of the sunnas that make up the prayer, for example. This is aided by the rigorously authenticated hadith that ‘A prayer that is not complete is added to from the supererogatory prayer associated with it until it is complete’. As for how the sunnas before the obligatory prayer cut the Devil from his greed, it is by their causing him to say ‘He didn’t leave what is not obligatory on him so how can he leave what is obligatory?’ [ Radd al-Muhtar `ala al-Durr al-Mukhtar, 1:452, Bulaq]

Ibn ‘Abidin explains, quoting the great Shafi`i faqih, Ibn Hajr al-Haytami, that the sunnas make up for the deficiency by standing the steed, in the next life, of obligatory prayers missed for excuses such as forgetfulness [s: though these prayers must still be made up].

There are a number of sunna prayers associated with each of the obligatory prayers.

Some of these are confirmed sunnas and some are non-confirmed sunnas.

A confirmed sunna (sunna mu’akkada) is something the Prophet (Allah bless him and give him peace) invariably did, leaving only occasionally. One is rewarded for doing it and deserves blame for leaving it without excuse. It is sinful to persistently leave it.

A non-confirmed sunna (sunna ghayr mu’akkada) is something the Prophet (Allah bless him and give him peace) did occasionally. There is a reward for doing it and no blame or sin for leaving it. [Shurunbulali, Maraqi al-Falah, 116, Maktaba al-‘Ilm al-Hadith]

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