أَوْ تُسْقِطَ ٱلسَّمَآءَ كَمَا زَعَمْتَ عَلَيْنَا كِسَفًا أَوْ تَأْتِىَ بِٱللَّهِ وَٱلْمَلَٰٓئِكَةِ قَبِيلًا

Or you should cause the heaven to come down upon us in pieces as you think, or bring Allah and the angels face to face (with us).