https://www.eislamicbook.com/virtual-currencies-ki-shari-haisiyat-by-muhammad-owais-paracha-%d9%88%d8%b1%da%86%d9%88%d8%a6%d9%84-%da%a9%d8%b1%d9%86%d8%b3%db%8c%d9%88%da%ba-%da%a9%db%8c-%d8%b4%d8%b1%d8%b9%db%8c-%d8%ad%db%8c%d8%ab/