Mother! I am about to become a mosque leader (4)
I believe the answer is:
imam
'a mosque leader' is the definition.
(I've seen this before)
'mother i am about' is the wordplay.
'mother' becomes 'mam' (I've seen this in other clues).
'i am' becomes 'i' (I've seen this in other clues).
'about' shows that the letters should be reversed in order.
'mam'+'i'='mami'
'mami' backwards is 'IMAM'.
'to become' is the link.
(Other definitions for imam that I've seen before include "Muslim prayer leader" , "Moslem prayer leader" , "Person leading devotions in a mosque" , "Muslim preacher" , "Muslim community leader" .)