Musnad Ahmad 1085:2

Rawh narrated to us, al-Awza'i narrated to us, from Abdullah ibn Sa'd, from al-Sanabahi, from a man among the companions of the Prophet, may God bless him and grant him peace, who said: "The Messenger of God, may God bless him and grant him peace, forbade the *ghulutat* (the pitfalls/traps)." Al-Awza'i said: The *ghulutat* are the difficult and arduous questions.