Handsome caliph denied last daughter to prophet (6)
I believe the answer is:
fatima
'daughter to prophet' is the definition.
(daughter of Muhammad)
'handsome caliph denied last' is the wordplay.
'handsome' becomes 'fat' (both can describe a generous amount).
'caliph' becomes 'imam' (both can mean a Muslim leader).
'denied last' means to remove the last letter (the word is denied its last letter).
'imam' with its last letter taken off is 'ima'.
'fat'+'ima'='FATIMA'
(Other definitions for fatima that I've seen before include "Place of Marian pilgrimage in Portugal" , "significant figure in Islam" , "Portuguese place of RC pilgrimage" , "I'm a fat girl of Islam" , "Portugese shrine or Muhammad's daughter" .)