Al-Kāfi
Hadith 2146عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ أَبِي عَبْدِ اللَّهِ عَنْ أَبِيهِ عَمَّنْ ذَكَرَهُ عَنْ أَيُّوبَ بْنِ الْحُرِّ عَنْ أَبِي حَمْزَةَ عَنْ أَبِي جَعْفَرٍ ( عليه السلام ) قَالَ إِنَّمَا قُصَّ الْأَظْفَارُ لِأَنَّهَا مَقِيلُ الشَّيْطَانِ وَ مِنْهُ يَكُونُ النِّسْيَانُ .
6. A number of our people have narrated from Ahmad ibn abu ‘Abd Allah from his father from those whom he has mentioned from Ayyub ibn al-Hurr from abu Hamzah who has said the following: “Abu Ja’far, Alayhi al-Salam, has said, ’There is clipping of fingernails; it reduces Satan; and because of it (unclipped fingernails) is forgetfulness.’”