Musnad Ahmad 32:1163

Yazid narrated to us, Jarir (meaning Ibn Hazim) informed us, from Qatadah, who said: I said to Anas ibn Malik: "How was the hair of the Messenger of Allah, peace and blessings of Allah be upon him?" He said: "It was wavy hair, neither straight nor curly, [falling] between his ears and his shoulders."