Nafl prayer

In Islam, a nafl prayer (Arabic: صلاة نفل‎‎, ṣalāt al-nafl) or supererogatory prayer is a type of optional Muslim salah (formal worship). As with sunnah prayer, they are not considered obligatory but are thought to confer extra benefit on the person performing them. An example is the offering of duha prayers. According to the following hadith, nafl not only draws one closer to God but also helps one attain the better success in the afterworld i.e. Paradise:

Tahiyatul wudu is the nafl prayer after doing wudhu.

Abu Hureyrah narrates that once Muhammad ﷺ asked Bilal at Fajr salah:

O Bilal!

Tell me that deed of yours which is most hopeful (for reward) after embracing Islam, for I heard your footsteps in front of me in Paradise (in my dream).

Bilal replied:

I have not done anything extra ordinary except that whenever I perform wudu during the day or night, I salah (tahiyatul wudu) after that, as much as was written or granted for me."

Abu Hureyrah narrated that Muhammad ﷺ said to Bilal

Tell me about the most hopeful act (i.e one which you deem the most rewarding with Allah) you have done since your acceptance of Islam because I heard the sound of the steps of your shoes in front of me in paradise.

Bilal said :

I do not consider any act more hopeful than that whenever I make ablution (wudu) at any time of night or day, I offer salah (prayer) for as long as was destined for me to offer.

After completion of the wudhu of two rakats is full of blessings (sawāb). It is related in the Hadith that performance of the two rakaats of Tahiyatul wudhu namaz makes paradise obligatory (wajib) for the performer (ref:Muslim Sharif) There are also many other benefits.

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Wikipedia