The verb "prove" is a copular(linking) verb in the below sentence:
The soundtrack of the movie proved to be a huge success.
See the following example from this site for reference:
GRAMMAR: Linking verbs
Prove is a linking verb in this meaning. This type of verb links the subject of the sentence with an adjective or noun:
The task proved difficult.
He has proved a loyal friend.
You can also say:
The task proved to be difficult.
He has proved to be a loyal friend.
The following search result from Google for "passive voice of copular verbs" clearly states that passive voice is not possible for the copular verb. Thus, the statement mentioned in this question can't be specified in the passive form.
Are linking verbs passive voice?
active voice: The guide lost the map. Verbs that are not action verbs are called stative verbs. Only action verbs have active or passive voice. Stative verbs are linking verbs and the verb “to be