Al-Kāfi - Volume 6 > Eating Clay
Hadith #2

عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدِ بْنِ خَالِدٍ عَنْ عُثْمَانَ بْنِ عِيسَى عَنْ طَلْحَةَ بْنِ زَيْدٍ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ أَكْلُ الطِّينِ يُورِثُ النِّفَاقَ .

2. A number of our people have narrated from Ahmad ibn Muhammad from ibn Khalid from ‘Uthman ibn ‘Isa from Talhah ibn Zayd who has said the following: “Abu ’Abd Allah, ‘Alayhi al-Salam, has said, ’Eating clay is of the sources of hypocrisy.”’