How can I repent and rectify my mistake after secretly taking a sum of money from my former partner, who claims to have incurred a loss, given that I am currently unable to inform him or return the money?

You must repent by returning the money you took from your partner without his knowledge. Your remorse is sufficient as part of your repentance, and you must return it, as the Prophet, peace be upon him, said: "On the hand is what it has taken until it returns it." If you do not possess it now, resolve to return it whenever you are able. You are not required to inform him of the reason; rather, it suffices to return it through indirect means. As for the whispers regarding your partner's purchase of properties, this is not sufficient to convict him of embezzling company funds without clear evidence. The word of the worker is accepted with his oath regarding what he claims of damage or loss.