Al-Kāfi - Volume 6 > Clipping the finger Nails
Hadith #15

عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ النَّوْفَلِيِّ عَنِ السَّكُونِيِّ قَالَ قَالَ رَسُولُ اللَّهِ ( صلى الله عليه وآله ) لِلرِّجَالِ قُصُّوا أَظَافِيرَكُمْ وَ لِلنِّسَاءِ اتْرُكْنَ فَإِنَّهُ أَزْيَنُ لَكُنَّ .

15. Ali ibn Ibrahim has narrated from his father from al-Nawfaliy from al-Sakuniy who has said the following: “He (the Imam), ‘Alayhi al-Salam, has said that the Messenger of Allah, O Allah, grant compensation to Muhammad and his family worthy of their services to Your cause, has said, ‘Men must clip their fingernails and women must keep them because it is more beautifying for them.’”