In this hadith: "Allaah 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.
Why is the 4 rakat Sunnah before Asr and Isha not included? Normally in prayer schemes these two are present but according to this hadith they are not.