What is the ruling on refusing to sponsor someone who is compelled to take out a bank loan for a heart surgery? Is refraining from doing good considered a sin? And what is the burden on the guarantor if he is compelled to undertake the sponsorship?

There is no blame on one who is compelled to borrow from a Riba-based bank and finds no other way to meet their necessity, due to the Almighty's saying: "And He has already explained to you what He has forbidden to you, except for that to which you are compelled." There is also no blame on one who guarantees this loan for them, because they are assisting them in what is permissible and helping them to obtain their need and relieve their distress.