Is the selling of a jointly owned car by one partner without the permission of the other partner considered a breach of trust, especially if the sale was due to people's grumbling and the partner's share was sent to him immediately?

A partner is not permitted to sell the share of his co-partner without the latter's permission, for the Prophet, peace and blessings be upon him, said: "Indeed, your blood, your properties, and your honors are sacred." Selling what one does not own is void. If he sells his share and his co-partner's share, the sale is valid only for what he owns. The buyer has the option [to revoke the sale] if he was unaware of this, and he is entitled to compensation for the defect if he chooses to keep [the purchased item].