Musnad Ahmad 1034:162

Waki’ narrated to us, Al-Awza’i narrated to us, from Yahya ibn Abi Kathir, from Abu Qilabah, who said: Abu Abdullah said to Abu Mas’ud, or Abu Mas’ud said to Abu Abdullah—meaning Hudhayfah—"What did you hear the Messenger of Allah, peace and blessings of Allah be upon him, say regarding 'they claim' (za’amu)?" He said: "I heard him say: 'It is an evil mount for a man.'"