Is it permissible to sell the share of fuel received from the government for the oven if it is not used and would otherwise be stolen?

If the condition for entitlement to the share is to operate the oven with it, then he is not permitted to take it for any other purpose, based on the hadith, "Muslims are bound by their conditions." However, if it is dispensed to him regardless, then there is no harm in him benefiting from it in the oven or otherwise. The fact that thieves might seize it does not permit him to take it unlawfully. If he is able to recover it from the thieves, he must return it to the concerned authority; otherwise, he should dispose of it for the general benefits and interests of the Muslims.