التفسير التبليغي
(And what will make you know what is Illiyyun?) (19)
Mujahid said: Illiyyun is in the seventh heaven. And it was said: it refers to the chambers of Paradise. And it was said: it is Sidrat al-Muntaha (the Lote Tree of the Utmost Boundary). And it was said: Illiyyun means an elevation upon an elevation, multiplied, as if it refers to the highest of places. Then it was pluralized with "waw" and "nun" to magnify its status.
(And what will make you know what is Illiyyun?) Its description cannot be encompassed by minds.
Source: التفسير التبليغي