The Prophet ﷺ used to dye his hair with henna and katam, and his hair reached down to his shoulders.
حدثنا عبد الله حدثنا محمد بن عبد الله المخرمي حدثنا أبو سفيان الحميري سعيد بن يحيى قال حدثنا الضحاك بن حمزة عن غيلان بن جامع عن إياد بن لقيط
كان النبي ﷺ يخضب بالحناء والكتم وكان شعره يبلغ كتفيه أو منكبيه
Its isnad is daif due to Dahhak bin Hamza Amluki Wasiti, whom they graded as daif because of his memory. As for Ghilan bin Jami bin Ashath Muharibi, the qadi of Kufa, he is trustworthy and his hadith appears in Muslim's collection. However, the hadith is sahih, having previously been given with fuller wording than this. See 13305 and 11904.