Al-Kāfi - Volume 6 > Eating Clay
Hadith #4

عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحَسَنِ بْنِ عَلِيٍّ عَنْ هِشَامِ بْنِ سَالِمٍ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ إِنَّ اللَّهَ عَزَّ وَ جَلَّ خَلَقَ آدَمَ مِنَ الطِّينِ فَحَرَّمَ أَكْلَ الطِّينِ عَلَى ذُرِّيَّتِهِ .

4. A number of our people have narrated from Ahmad ibn Muhammad from al-Hassan ibn Ali from Hisham ibn Salim who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that Allah, most Majestic, most Glorious, created Adam from clay and has made it unlawful for his offspring to eat clay.’”