Al-Kāfi - Volume 6 > The Milk Products
Hadith #4

الْحُسَيْنُ بْنُ مُحَمَّدٍ عَنِ السَّيَّارِيِّ عَنْ عُبَيْدِ اللَّهِ بْنِ أَبِي عَبْدِ اللَّهِ الْفَارِسِيِّ عَمَّنْ ذَكَرَهُ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ قَالَ لَهُ رَجُلٌ إِنِّي أَكَلْتُ لَبَناً فَضَرَّنِي قَالَ فَقَالَ لَهُ أَبُو عَبْدِ اللَّهِ ( عليه السلام ) لَا وَ اللَّهِ مَا يَضُرُّ لَبَنٌ قَطُّ وَ لَكِنَّكَ أَكَلْتَهُ مَعَ غَيْرِهِ فَضَرَّكَ الَّذِي أَكَلْتَهُ فَظَنَنْتَ أَنَّ ذَلِكَ مِنَ اللَّبَنِ .

4. Al-Husayn from Muhammad has narrated from al-Sayyariy from ‘Ubayd Allah ibn abu ‘Abd Allah al-Farsiy from those whom he has mentioned who has said the following: “Once, a man said to abu ‘Abd Allah, ‘Alayhi al-Salam, ‘I eat milk products and they harm me.’ Abu ‘Abd Allah, ‘Alayhi al-Salam, said to him, ‘No, by Allah, milk never harms; but you may have eaten something else with it which has harmed you, but you thought it is milk.’”