Salat al-Asr (Afternoon)

The Afternoon Contact Prayer (Salat al-Asr) is referenced in two verses. 11:114 indicates that this is one of the two ends of the day.

[11:114] You shall observe the Contact Prayers (Salat) at both ends of the day, and during the night. The righteous works wipe out the evil works. This is a reminder for those who would take heed.

وَأَقِمِ ٱلصَّلَوٰةَ طَرَفَىِ ٱلنَّهَارِ وَزُلَفًا مِّنَ ٱلَّيْلِ إِنَّ ٱلْحَسَنَـٰتِ يُذْهِبْنَ ٱلسَّيِّـَٔاتِ ذَٰلِكَ ذِكْرَىٰ لِلذَّٰكِرِينَ

The Afternoon Contact Prayer is known as the Middle Contact Prayer (Salat al-Wusta) because it begins at the halfway point between when the sun begins its decline from noon to sunset.

[2:238] You shall consistently observe the Contact Prayers, especially the middle prayer, and devote yourselves totally to GOD.

حَـٰفِظُوا۟ عَلَى ٱلصَّلَوَٰتِ وَٱلصَّلَوٰةِ ٱلْوُسْطَىٰ وَقُومُوا۟ لِلَّهِ قَـٰنِتِينَ

Dr. Rashad Khalifa also clarifies this point in a brochure published and distributed during his last submitter's conference in 1989.