before

Assalam Alaikkum, Do we need to sleep before Thahajjud prayer? Some times I go to sleep very late in the weekends, so I offer thahajjud and witr before I go to sleep and gets up at the time of fajr since there is no time to sleep before doing night prayer. Is this allowed?

Respected scholars, As-salamu `alaykum. In one masjid here, I saw people praying two nafl (optional) rak`ahs immediately after the Adhan of Maghrib, but before the fard salah (pres cribed prayer). Is this practice correct? Jazakum Allahu khayran.