Ibn ‘Abbās and others said:

“In a circle, like the whorl of a spindle.”

In the hadith narrated by Jubayr ibn Mut‘im from the Prophet (may Allah bless him and grant him peace), recorded by Abū Dāwūd, al-Tirmidhī and others, it is related:

“A Bedouin said, ‘O Messenger of Allah, people are exhausted, families are hungry, and livestock have perished. Pray to Allah for us, for we seek your intercession with Allah, and Allah’s intercession with you.’ The Messenger of Allah (may Allah bless him and grant him peace) then glorified Allah until the effect of this could be seen on the Companions’ faces. Then he said, ‘Woe to you! Do you know who Allah is? Allah’s majesty is far greater than that. None of His creation may seek intercession through Allah. His Throne is above His heavens like this’—and he shaped his fingers like a dome—‘and it indeed creaks beneath Him as a new saddle creaks beneath its rider.’”

This is discussed at length elsewhere.

Since the opponent has himself adduced this as evidence, it constitutes an argument against him. If the world is spherical—and it is necessarily established that He must either be within it or separate from it, and He is not within it—then He must be separate from it. If He is separate from it, He must be above it, since ‘above’ can only be the encompassing sphere and whatever lies beyond it.