Al-Kāfi - Volume 6 > Clipping or Pulling out Gray Hairs
Hadith #3

عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنِ النَّوْفَلِيِّ عَنِ السَّكُونِيِّ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) أَنَّ أَمِيرَ الْمُؤْمِنِينَ ( عليه السلام ) كَانَ لَا يَرَى بِجَزِّ الشَّيْبِ بَأْساً وَ يَكْرَهُ نَتْفَهُ .

3. Ali ibn Ibrahim has narrated from his father from al-Nawfaliy from al-Sakuniy who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said that ’Amir al-Mu’minin did not consider it harmful to clip gray hairs but disliked pulling it out.’”