«فَهَلْ سَمِعْتُمْ يَا أُولِي الْأَلْبَابِ بِأَعْجَبَ مِنْ هَذَا الْعُجَابِ؟»
People of understanding, have you heard of anything more astonishing than this marvel?
Ulū al-albāb means people of sound intellect; ʿujāb means something exceptionally wondrous. The cognate link aʿjab / al-ʿujāb intensifies the challenge.
This is chiefly a rhetorical question of amazement: Abū Zayd seeks the audience’s emotional agreement that his story is unparalleled, not fresh information about other anecdotes.
The audience answers «لَا، وَمَنْ عِنْدَهُ عِلْمُ الْكِتَابِ»: No, by Him who has the knowledge of the Book. The oath expresses wonder, not proof of lineage.