save big money if any received to create financial/economic security

occasions do come in life when a man or woman receives a certain amount of unexpected big money like arrears of salary,promotion hikes,recovery of past debts etc...On such occasions it makes sense to create financial/ecocomic security by keeping such money in fixed deposits or post office monthly income or open a recurring deposit in bank or post office etc.The bank deposits if made can be made either for monthly interest or for interst on maturity