The Challenge to Produce Evidence

أَمْ لَهُمْ سُلَّمٌ يَسْتَمِعُونَ فِيهِ ۖ فَلْيَأْتِ مُسْتَمِعُهُم بِسُلْطَـٰنٍ مُّبِينٍ

Or have they a stairway [into the heaven] upon which they listen? Then let their listener produce a clear authority [i.e., proof].