Al-Kāfi - Volume 6 > Clipping the finger Nails
Hadith #2

عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ ابْنِ أَبِي عُمَيْرٍ عَنْ هِشَامِ بْنِ سَالِمٍ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ تَقْلِيمُ الْأَظْفَارِ يَوْمَ الْجُمُعَةِ يُؤَمِّنُ مِنَ الْجُذَامِ وَ الْبَرَصِ وَ الْعَمَى وَ إِنْ لَمْ تَحْتَجْ فَحُكَّهَا .

2. Ali ibn Ibrahim has narrated from his father from ibn abu ‘Umayr from Hisham ibn Salim who has said the following: “Abu ‘Abd Allah, Alayhi al-Salam, has said, ’Clipping fingernails on Fridays is immunity from leprosy, albinism and blindness. If you do not need clipping then just scratch them.’”