Are the profits I earned from my work at a charity, in cooperation with my partner, Islamically permissible, taking into account my consultation with scholars and obtaining their permission, and my salary which I receive from the charity?

It is impermissible for an agent to purchase from their company without the permission of their principal, based on the opinion of the majority of scholars. However, since the purchase has already taken place, and there was no favoritism shown to your company, the contract is considered valid to ensure the stability of transactions. Nevertheless, you must not repeat this in the future.