Is it permissible for the bank to cover the expenses of an operation and treatment for the patient's father, who suffers from Alzheimer's, knowing that he is a former employee of an agricultural development and credit bank and is 76 years old?

Working in a Riba-based bank is Haram, and its salary is Haram. The retirement pension resulting from it is Haram. However, it becomes permissible if the father was ignorant of the prohibition of working in a Riba-based bank or believed it to be permissible based on the fatwas of scholars in his country. But if he knew of the prohibition and continued to work, then it is not permissible for him to benefit from the retirement pension. He must donate it as charity or spend it on public Muslim welfare, unless it matches the pension of his peers among the elderly, in which case he should donate the excess. It is obligatory for capable children to financially support their needy father to prevent him from reverting to Haram money. If they are unable to do so, it is permissible for him to request money from the bank when in need.