Mishkat al-Masabih 4550
Zuhri reported in mursal form that the Prophet said:
“If anyone has himself cupped on a Wednesday or a Saturday and is smitten by leprosy, he must blame no one but himself .” 

Ahmad and Abu Dawud transmitted it. 
It has been given an isnad , but Abu Dawud said that that is not sound;
وَعَنِ الزُّهْرِيِّ مُرْسَلًا عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «مِنْ احْتَجَمَ يَوْمَ الْأَرْبِعَاءِ أَوْ يَوْمَ السَّبْتِ فَأَصَابَهُ وَضَحٌ فَلَا يَلُومَنَّ إِلَّا نَفْسَهُ» . رَوَاهُ أَحْمَدُ وَأَبُو دَاوُدَ وَقَالَ: وَقَدْ أسْند وَلَا يَصح