Translation:

238. Guard strictly your (habit of) prayers especially the middle prayer and stand before Allah in a devout (frame of mind).

Notes (Tafseer)

271. The Middle Prayer: Salutul-wusta: may be translated "the best or the most excellent prayer." Authorities differ as to the exact meaning of this phrase. The weight of authorities seems to be in favour of interpreting this as the 'Asr prayer in the middle of the afternoon. This is apt to be most neglected, and yet this is the most necessary, to remind us of God in the midst of our worldly affairs. There is special Sura, entitled 'Asr, of which the mystic meaning is appropriately dealt with under that Sura.