Salah is divided into four groups such as fardh (obligatory), wajib (required), sunnah and nafilah. There are two kinds of sunnah such as emphasized (al-Muakkadah) and non-emphasized (al-Ghayr'muakkadah).
Al-nafilah has a lot of types. They are awwabin, duha, thahajjud, tasbih and so on.
Awwabin: There are a hundred divine merits in the performance of Salat al-Awwabin. Allah, the Supreme Being, grants seventy-five merits to His slaves in the Hereafter and twenty-five merits in this worldly life. Accordingly, those who continue to perform Salat al-Awwabin do not meet with any hardship on the Day of Judgement.
Salat al-Awwabin is performed in six rakahs after the Sunset Prayer (salat al-Maghrib).