What is the ruling on children taking the savings passbooks their father gave them after a long separation, knowing that their father did not spend on them previously, and the source of his money may be mixed between pension and usury? Is it permissible for them to refuse future interest, or to donate it, or to use it to pay off debts? Is it permissible for them to take only the original deposit? And is the food and clothing their father buys considered unlawful if the source of his money is mixed?

There is no harm for the children in accepting deposits and benefiting from their principal if it is clearly defined. As for the interest, if it is usurious, it is not permissible to benefit from it. It should be given to the poor and needy or for the general welfare of Muslims, unless the children themselves are poor, in which case it is permissible for them to take it to fulfill their needs. However, if the deposits are in an Islamic bank, then it is permissible to benefit from their profits. Ignorance of the source of money or fear that it was acquired from unlawful means does not prevent benefiting from it, for the unknown is like the non-existent, and the basic principle is that what is in a Muslim's possession is his property.