Can interest money be used to pay for hospital bills?
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
As a principle, it is impermissible to engage in interest bearing transactions. Allah the Almighty has vowed to wage war with the one who deals with interest. You must do all that is in your capacity to free yourself from engaging in interest.
Any interest money you have in your possession must be dispensed off without the intention of attaining reward; instead you will be merely ridding yourself from impure funds.
One cannot benefit from interest money. It is totally impure. Interest money must be given to those poor people who are eligible to receive Zakāt.
Thus, it is not permissible to use interest funds to pay one’s hospital bill. Use halāl wealth to pay for one’s needs. This will result in barakah (blessings) and will attract the Mercy of Allah Ta’ālā.
And Allah Ta’ālā Knows Best
Mufti Faraz al-Mahmudi,
 وَيَرُدُّونَهَا عَلَى أَرْبَابِهَا إنْ عَرَفُوهُمْ، وَإِلَّا تَصَدَّقُوا بِهَا؛ لِأَنَّ سَبِيلَ الْكَسْبِ الْخَبِيثِ التَّصَدُّقُ إذَا تَعَذَّرَ الرَّدُّ عَلَى صَاحِبِهِ. (تبيين الحقائق ج 6 ص 27 مكتبة بولاق)
وكذا في فتاوى محمودية ج 16 ص 382 إدارة الفاروق