Al-Kāfi - The Book of Food

َّرِ بْنِ خَلَّادٍ عَنْ أَبِي الْحَسَنِ ( عليه السلا٠) قَالَ قُلْتُ لَهُ ٠َا يَرْوِي النَّاسُ فِي أَكْلِ الطِّينِ وَ كَرَاهِيَتِهِ فَقَالَ إِنَّ٠َبْلُولُ وَ ذَاكَ الْ٠7.

Ahmad ibn Muhammad has narrated from Mu’ammar ibn Khallad who has said the following: “I once asked abu al-Hassan (a.s.), about what people narrate as regards eating clay and that it is undesirable. He (the Imam) said, ‘It is clay and chunks of dirt.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (22/65))