Sunan an-Nasa'i 5243
It was narrated that 'Ubaid said:
"I saw Ibn 'Umar dyeing his beard yellow and I asked him about that. 'He said: "I saw the Prophet [SAW] dye his beard yellow."
أَخْبَرَنَا يَحْيَى بْنُ حَكِيمٍ، قَالَ حَدَّثَنَا أَبُو قُتَيْبَةَ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ عُبَيْدٍ، قَالَ رَأَيْتُ ابْنَ عُمَرَ يُصَفِّرُ لِحْيَتَهُ فَقُلْتُ لَهُ فِي ذَلِكَ فَقَالَ رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم يُصَفِّرُ لِحْيَتَهُ ‏.‏