Musnad Ahmad 1034:215

Abu Nu'aym narrated to us, Sufyan narrated to us, from 'Umar ibn Muhammad, from 'Umar, the freed slave of Ghafrah, from a man of the Ansar, from Hudhayfah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, every nation has its Magians, and the Magians of this nation are those who say there is no decree (Qadar). So whoever among them falls ill, do not visit him, and whoever among them dies, do not attend his funeral. They are the partisans of the Dajjal; it is a right upon Allah to attach them to him."