Al-Kāfi - Volume 3 > Placing the Forehead on the Ground
Hadith #9

9ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ فَضَالَةَ عَنْ أَبَانٍ عَنْ عَبْدِ الرَّحْمَنِ بْنِ أَبِي عَبْدِ الله قَالَ سَأَلْتُ أَبَا عَبْدِ الله (عَلَيْهِ الْسَّلام) عَنِ الرَّجُلِ يَسْجُدُ وَعَلَيْهِ الْعِمَامَةُ لاَ يُصِيبُ وَجْهُهُ الأرْضَ قَالَ لاَ يُجْزِئُهُ ذَلِكَ حَتَّى تَصِلَ جَبْهَتُهُ إِلَى الأرْضِ.

9. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from al-Husayn ibn Sa‘id from Fadalah from Aban from ‘Abd al- Rahman ibn abu ‘Abd Allah who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about a man who performs Sajdah (prostration) wearing a turban which prevents his face from falling on the earth. He (the Imam) said, ‘No, it is not sufficient until his forehead touches the earth.’”