Al-Kāfi - Volume 3 > Sprucing up on Fridays
Hadith #10

10ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ ابْنِ فَضَّالٍ عَنِ ابْنِ بُكَيْرٍ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ غَسْلُ الرَّأْسِ بِالْخِطْمِيِّ فِي كُلِّ جُمُعَةٍ أَمَانٌ مِنَ الْبَرَصِ وَالْجُنُونِ.

10. A number of our people have narrated from Ahmad ibn Muhammad from ibn Faddal from ibn Bukayr who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said, ‘Washing one’s head with marshmallow every Friday is protection against leprosy and insanity.’” (The following chapters are best explained by fatwa.)