1- Is expiation obligatory for one who swore not to let a person enter the mosque, then that person entered it and prayed therein? 2- What is the ruling on money earned from a usurious loan, and how can it be purified?

If children enter the mosque, then a person who swore an oath that they would not enter must pay expiation for the oath. Expiation is also due from one who swore an oath that the person preventing the children from entering would not enter if they entered the mosque, unless the intention was that they would not enter if the children did not enter, and then they did enter, in which case there is nothing upon him. As for borrowing with interest, it is forbidden and not permissible except in cases of necessity and only to the extent of that necessity.