Sleeping between Asr and Maghrib is Makrooh for ordinary Muslims, as their is a risk that they will delay their Maghrib Salaah.
Khawat Bin Jubair Radi Allahu Anho has said “Sleeping at day break (after Fajr) is a lack of wisdom, sleeping at Midday (after Dhuhr) is a (good) habit and sleeping at sunset (Before Maghrib) is foolishness. (Bukhari)
There is also a weak narration from Aisha Radi Allahu Anha who said “Whoever sleeps after Asr Salaah and loses their intellect, has only themselves to blame”.
However, it is not Haraam as the Messenger of Allah had slept on the lap of Sayyiduna Ali when the miracle of turning back the sun was performed.
Therefore, for scholars, when there is need, it is permissable as long as provision is made to get up for Maghrib.
Allah knows best
[Answer provided by: Muhammad Salim Ghisa]