The Quran

وَما نَتَنَزَّلُ إِلّا بِأَمرِ رَبِّكَ ۖ لَهُ ما بَينَ أَيدينا وَما خَلفَنا وَما بَينَ ذٰلِكَ ۚ وَما كانَ رَبُّكَ نَسِيًّا

Muhammad Asad

AND [the angels say]: "We do not descend [with revelation], again and again, other than by thy Sustainer's command: unto Him belongs all that lies open before us and all that is hidden - from us and all that is in-between.¹ And never does thy Sustainer forget [anything] -

I.e., that which even the angels can only glimpse but not fully understand. Literally, the above phrase reads, "that which is between our hands and that which is behind us and that which is between these". Regarding this idiomatic expression, see 2:255 - "He knows all that lies open before men and all that is hidden from them" - and the corresponding note 247. The reference to the angels connects with the preceding mention of some of the earlier prophets who, like Muhammad, were recipients of divine revelation.