Against Muhammad bearing overnight case? (6)
I believe the answer is:
valise
'overnight case?' is the definition.
(valise is a kind of overnight case)
'against muhammad bearing' is the wordplay.
'against' becomes 'v' (abbreviation for 'versus').
'muhammad' becomes 'ali' (I've seen this in another clue).
'bearing' becomes 'se' (south east, a compass bearing).
'v'+'ali'+'se'='VALISE'
(Other definitions for valise that I've seen before include "Overnight case" , "Small piece of luggage" , "Small overnight bag" , "Elvis A? (anag)" , "A small suitcase for Leavis" .)