Is it permissible for me to keep a large sum of money, exceeding my salary, that was deposited into my bank account under the category "consultations," even though I did not provide any consultations?

You are not permitted to take the extra money without consulting your workplace and inquiring about the reason for the increase, because you know that you are not entitled to it. If your workplace informs you that it is a gift, then there is no harm in you benefiting from it. Otherwise, you must return it, for the Prophet, peace and blessings be upon him, said: "The hand is responsible for what it has taken until it returns it."