Is it permissible to take and benefit from borrowed money after the lender intended to donate it to the borrower, but without informing him of this intention, and then the lender became in need of this money upon its repayment?

The questioner is not obligated to return the money to its owner because what transpired in his mind — the intention of a gift or charity — was neither verbalized nor acted upon. The Messenger of Allah, peace and blessings be upon him, said: "Indeed, Allah has pardoned for my Ummah what they whisper to themselves, as long as they do not speak of it or act upon it."