Is it permissible to reclaim gold that was given to someone for investment with a 50% share of the profits, after discovering that it was invested in something other than what was agreed upon, by taking an equivalent value from him, knowing that there is no other way to recover the money?

Mudarabah with gold is not permissible because the capital for Mudarabah must be in cash. If such a Mudarabah occurs, it is invalid, and the agent is entitled to a fair wage (ujrat al-mithl), while all the profit belongs to the gold owner. If the agent acts contrary to the agreed-upon condition, he becomes an aggressor against the capital owner's property and is liable for it.

If the agent denies the debt or withholds it, it is permissible to demand it through legitimate means, such as litigation. If the questioner knows that the ruler or others cannot restore his right, it is permissible for him to take it from the agent, even without his permission, especially if the denier is procrastinating and cannot be compelled to go to trial. The questioner should recover the value of the gold owed to him from the amount in the agent's possession and return any excess.