A religious decree issued by a Muslim leader (5)
I believe the answer is:
fatwa
'a religious decree issued by a muslim leader' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fatwa that I've seen before include "death sentence?" , "Ruling by Islamic religious leader, say Ayatollah" , "Legal ruling by Islamic leader, as against Salman Rushdie" , "Muslim decree or formal legal judgement" , "threat" .)