وَعَنْهُ مُرْسَلًا قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مَنِ احْتَجَمَ أَوِ اطَّلَى يَوْمَ السَّبْتِ أَوِ الْأَرْبِعَاءِ فَلَا يَلُومَنَّ إِلَّا نَفْسَهُ فِي الوَضَحِ» . رَوَاهُ فِي شرح السّنة

“If anyone has himself cupped or smeared with something on a Saturday or a Wednesday, he must blame no one but himself if he gets leprosy.” It is transmitted in Sharh as-sunna.