What is the ruling on working as an accountant for clients who sell pork and deal in usury, and what is the ruling on writing letters used in usurious loans? Is the money earned from this work permissible, and is it permissible to invest it or perform Hajj with it?

It is forbidden to work in recording usury, calculating it, or writing its transactions, because it involves cooperating in sin. Whoever repents from illicit earnings must dispose of the money by spending it on charitable causes, unless they are in need, in which case they may take what they need and donate the rest. If part of the work is permissible and part is forbidden, the percentage of the forbidden must be estimated and the corresponding amount of money disposed of. If estimation is difficult, then half of it should be disposed of.