Musnad Ahmad 30:2409

Yahya ibn Sa'id narrated to us, from 'Awf, who said: Khallas narrated to me, from Abu Hurayrah and al-Hasan, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever goes to a soothsayer or a diviner and believes him in what he says, then he has disbelieved in what was revealed to Muhammad."