Is taking part of the interest from usurious banks as a loan to buy a computer, with the intention of repaying it in a charitable act (such as printing religious booklets), considered Riba (usury)? And if so, how can this money be purified, given that the income barely covers living expenses and medical treatment? And does Allah accept the purification of a grandfather's money from usurious interest after his death?

It is forbidden to deposit money in usurious banks, whether one takes the interest or donates it, due to the affirmation and assistance it provides to usury. The Messenger of Allah (peace and blessings be upon him) "cursed the one who consumes usury, the one who pays it, its scribe, and its two witnesses, and he said: 'They are all equal.'"

The money must be withdrawn immediately, and the interest must be disposed of by spending it on general Muslim welfare. The amount of interest spent on purchasing the computer should be replaced with an equivalent amount of lawful money.

True security lies in piety and obedience to Allah, and "whoever fears Allah - He will make for him a way out and will provide for him from where he does not expect." Good intentions do not justify engaging in usury, and the true future is the grave and what comes after it. It is imperative to advise and warn your grandfather about the gravity of usury.