What is the ruling on someone who found a sum of money in their bank account, was in dire need of it, spent it on lawful and good causes, and pledged to the bank to repay this money through monthly installments?

If a person finds a sum of money in their bank account by mistake, it is not permissible for them to take it. They must inform the officials and return the money to its owner, based on Allah’s saying: ﴿Indeed, Allah commands you to render trusts to whom they are due﴾ [An-Nisa: 58], and His saying: ﴿And do not consume one another's properties unlawfully﴾ [Al-Baqarah: 188]. This is also because a Muslim's wealth is sacred, like the sanctity of the Day of Arafah. Whoever takes the money and benefits from it, then returns it in installments, has committed a sin. They must repent and seek forgiveness from the bank officials. It is permissible to deal with Islamic banks that adhere to Sharia regulations, but it is not permissible to deal with interest-based banks.