Fiqh-us-Sunnah - 2.1

Hadith 2.1.1

Their significance

At-tatawwu', or nawafil or supererogatory prayers, have been legislated to make up for any deficiencies left in the performance of fard salah (obligatory prayers). In salah, there are virtues that are not found in any other form of worship. Abu Hurairah reports that the Prophet sallallahu alehi wasallam said: "The first thing that the people will be called to account for on the Day of Resurrection will be the prayers. Our Lord will say to the angels although He knows better: 'Look into the salah of my servant to see if he observed it perfectly or been negligent in it. So if he observed it perfectly it will be recorded to his credit, but if he had been negligent in it in any way, Allah would say: See if My servant has any supererogatory prayers. Then if he has any supererogatory prayers, Allah would say: Make up the deficiency in My servant's obligatory prayer with his supererogatory prayers.' Thereafter all his actions will be examined in like manner" (Abu Dawud).
Abu Umamah narrates that the Prophet sallallahu alehi wasallam said: "Allah does not listen to anything from His slave as He does to the two rak'at (of prayer) that he offers. Mercy descends over the servant's head as long as he remains in prayer" (Ahmad and at-Tirmidhi).
As-Sayuti grades it sahih. In al-Muwatta', Malik says: "It has reached me that the Prophet said: '(Try to) keep to the straight path although you won't be able to do so completely; and know that the best of your deeds is the salah, and only a (true) believer preserves his wudu.'" Muslim records from Rabi'ah ibn Malik al-Aslami that the Prophet sallallahu alehi wasallam said: "Ask (anything)."
Rabi'ah said: "I ask of you to be your companion in paradise." The Prophet said: "Or anything else?" Rabi'ah said: "That is it." The Prophet sallallahu alehi wasallam said to him: "Then help me by making many prostrations (i.e., supererogatory prayers)."