Al-Kāfi - Volume 6 > The Black Dye and Woad
Hadith #2

عَنْهُ عَنِ ابْنِ مَحْبُوبٍ عَنْ عَبْدِ اللَّهِ بْنِ سِنَانٍ قَالَ سَأَلْتُ أَبَا عَبْدِ اللَّهِ ( عليه السلام ) عَنِ الْوَسِمَةِ فَقَالَ لَا بَأْسَ بِهَا لِلشَّيْخِ الْكَبِيرِ.

2. It is narrated from the narrator of the previous Hadith from ibn Mahbub from ‘Abd Allah ibn Sinan who has said the following: “I once asked abu ‘Abd Allah, ‘Alayhi al-Salam, about applying Woad. He (the Imam) said, ‘It is not harmful to an old man ."