Hadithcore
Ash-Shama'il Al-Muhammadiyah, 49

Hammad said:

'Abdullah ibn Muhammad ibn 'Uqail also informed us: "I saw the hair of Allah’s Messenger (ﷺ) dyed in the presence of Anas ibn Malik."

قَالَ حَمَّادٌ : وَأَخْبَرَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدِ بْنِ عَقِيلٍ قَالَ : رَأَيْتُ شَعْرَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عِنْدَ أَنَسِ بْنِ مَالِكٍ مَخْضُوبًا

References1 variant
In-Book Reference
Book 6, Hadith 5