Al-Kāfi
Hadith 23378ـ عَنْهُ عَنْ أَحْمَدَ بْنِ مُحَمَّدِ بْنِ أَبِي نَصْرٍ عَنْ أَبِي الْحَسَنِ الرِّضَا (عَلَيهِ السَّلام) أَنَّهُ كَانَ يُتَرِّبُ الْكِتَابَ وَقَالَ لا بَأْسَ بِهِ.
8. It is narrated from him (narrator of the Hadith above) from Ahmad ibn Muhammad ibn abu Nasr who has said the following: “Abu al-Hassan al-Rida (a.s.) would dry up the ink on a newlywritten letter by means of placing soil on it and would say that doing so is not an offense.”