Is it permissible to take a loan, with the intention of paying it back, from money whose source is bank interest, or is it permissible to take it as charity, knowing that the borrower needs the money to complete the building of his house?

The benefits a wealthy person gains from usury (riba) are forbidden and cannot be accepted as charity. Such a person must spend this money on things that benefit Muslims, with the intention of getting rid of it, not as an act of devotion. A poor person is permitted to take this money because its prohibition applies only to the one who earned it, and there is no sin upon the poor person for taking it.