What is the ruling on receiving a large sum of money in a bank account, then transferring it to another account for a commission, without knowing the source of the money, despite knowing the sender?

If the money is unlawful, such as drug money, then accepting the offer is not permissible, because it is a means of spreading corruption, facilitating the unlawful, and concealing evil. This constitutes money laundering. Allah Almighty said: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression). If the source of the money is unknown, it is not permissible to undertake the work until the source of the funds is known and it becomes clear that the matter is free from anything unlawful.