Jami At-Tirmidhi 2982–Abu Yunus, the freed slave of Aishah, said: “Aisha ordered me to write a Mushaf for her, and she said: ‘When you get to this Ayah then tell me: Guard strictly (the five obligatory) prayers, and the middle Salat.’ So when I reached it, I told her and she dictated to me: ‘Guard strictly (the five obligatory) prayers, and the middle Salat, and Salat Al-Asr. And stand before Allah with obedience.’ She said: ‘I heard that from the Messenger of Allah.'”
Response:
It is not the part of verse but it was the elaboration by Prophet Muhammad s.a.w.w. that Salatil wusta is the Prayer of Asr.
Read the following hadees.
Narrated Samurah bin Jundab:
“The Prophet of Allah (ﷺ) said: ‘The middle Salat is Salat Al-‘Asr.'”(Tirmizi)
Rebuttal to Answering Muslims 