Nobody is questioning the source of funds for the balance in a bank account that’s been there for forty years. OP could literally just put it in the bank, sit

Nobody is questioning the source of funds for the balance in a bank account that’s been there for forty years. OP could literally just put it in the bank, sit on it for a year, and there’d be zero questions. They are mostly only interested in knowing that you didn’t get this money from a different loan that they aren’t aware of (like a personal loan, or one you got two days ago that hasn’t yet been reported).