Claim without proof (6)
I believe the answer is:
allege
'claim without proof' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for allege that I've seen before include "Declare without absolute proof" , "Assert, state without proof" , "Accuse without established proof" , "State as a fact without proof" , "Swear" .)