Is the extra money spent by mistake permissible or forbidden?

Working in interest-based banks is forbidden unless there is an urgent necessity, in which case one must seek lawful employment.

Salary earned from unlawful work must be disposed of by spending it on charitable causes and public welfare. It is permissible for a poor person to take from it according to his need.

If you were not aware of the impermissibility of the work previously, there is no sin in benefiting from what you have already received, but disposing of it is more cautious.

If a salary is disbursed twice by mistake, it must be returned to the bank if possible; otherwise, it should be spent on charitable causes.