Allah will build a house in Heaven for whoever is diligent in observing 12 Sunnah Rak'aat, called Sunnah Rawaatib.
(A version of this is at Islam Q&A.)
What are Sunnah Rawaatib?
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The 12 sunnah e muakaddah prayers in the whole day.
"Allah will build a house in Heaven for whoever is diligent in observing 12 Sunnah Rak'aat (as follows): 4 Rak'aat before and 2 after the Dhuhr (Midday) Prayer, 2 after the Maghrib (Sunset Prayer), 2 after the ‘Ishaa’ (Evening) Prayer and 2 before the Fajr (Dawn) Prayer." Hadith sahih narrated by at-Tirmidhi No. 379 and by others. Hadith No. 6183 in Sahih al-Jaami’
Basically as sunnan ar-rawatib السنن الرواتب are sunah or optional prayers related to a mandatory prayer.
And you are recommended to perform them.
Note that different ahadith quote different amounts of rak'at of these sunnan especially for dhor and maghrib. Here some references (Sahih al-Bukhari; Jami' at-Tirmdihi, Sunan an-Nasa-i, Sunan ibn Majah, Sunan abi-Dawod) for different statements.
Some madhabs stick on a certain amount and form.
Here a fatwa in Arabic (islamweb #275101) on the issue.