Prove to be incorrect (6)
I believe the answer is:
refute
'prove to be incorrect' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for refute that I've seen before include "Rebut; deny" , "Contradict, prove that statement is wrong" , "Prove that statement or accusation is wrong" , "Negate" , "Prove something to be wrong" .)