Moslem leader said to be virtuous (5)
I believe the answer is:
moral
'virtuous' is the definition.
('moral' can be similar in meaning to 'virtuous')
'moslem leader said' is the wordplay.
'leader' says to take the initial letters.
'said' becomes 'oral' (I've seen this before).
The initial letter of 'moslem' is 'm'.
'm'+'oral'='MORAL'
'to be' is the link.
(Other definitions for moral that I've seen before include "Lesson of a fable" , "Righteous" , "Honourable" , "Upright; message of fable" , "knowing right from wrong" .)