What is the ruling of the Sharia on the amount of money taken by the questioner from the client for a design that was not implemented due to the unavailability of the model, and is he obligated to return the full amount or a third of it, especially since his former partners refuse to bear responsibility?

A partnership of bodies (sharikat al-abdan) is valid. This occurs when two or more people jointly undertake a task that they accept as their responsibility, even if their crafts differ. Whatever one of them undertakes becomes the responsibility of both, and they are both accountable for it and obliged to perform it. A non-expert must appoint someone to act on his behalf. Each partner has the right to demand payment, and the hirer may pay either of them. If the payment is lost while in the possession of one of them, without negligence, it is the responsibility of both. If the client requesting the design is unaware of the partnership, the one who accepted the work will be held accountable, and then he will refer back to his partners.