﴿ بِأَييِّكُمُ ٱلْمَفْتُونُ ﴾

“which of you was bereft of reason.”

which of you is demented al-maftūn is a verbal noun similar in expressional form to al-ma‘qūl ‘intelligible’; al-futūn meaning al-junūn ‘insanity’ in other words is it this insanity in you or in them?