Answer
We have not come across any prohibition in Shari?ah sources for sleeping between Asr and Maghrib Salaat.
However, in general, if one fears oversleeping and missing Maghrib Salaat, then he should not sleep after Asr Salaat. The time for Maghrib ends when the red twilight in the horizon disappears.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai