As Salat Al Wusta is the Asr prayer. In an authentic Hadith, the prophet (Sallallahu Alayhi Wasallam) said during the battle of Khandaq: “…they have prevented us from offering the middle prayer ( i.e. Asr prayer) …{Bukhari} . Meaning the Asr prayer. “Wusta” literally means the middle number, but here it means the best.