Salat-ul-Awwabin (Prayer of the Repentant)
After performing the fard and sunnah of Maghrib, one may perform from 6 to a maximum of 20 rak’ât nafl. This prayer has been called as Awwâbîn. (This name is sometimes also applied to the morning prayer.)
The Prophet ( saws) reportedly said:
“Whoever prays, after the Maghrib, six rak’ât without talking of anything indecent in between them, it would be equivalent to twelve years of worship for him.” [M1173, from Tirmidhi]
“The one who prays twenty rak’ât after Maghrib- Allâh will build for him a house in Paradise.” [M-1174, from Tirmidhi]
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The first hadeeth is not authentic and it is very weak.
The second hadeeth is fabricated and a lie.