Andrean, R., and H. H. Adinugraha. “Competency Problems of Halal Slappers In Indonesia: A Literature Study”. Al - Muamalat: Jurnal Hukum Dan Ekonomi Syariah, Vol. 6, no. 1, June 2021, pp. 1 - 13, https://journal.iainlangsa.ac.id/index.php/muamalat/article/view/3525.