Musnad Ahmad 27:204

Yahya narrated to us, from Malik, Zayd ibn Aslam narrated to us, I heard Ibn Umar saying: Two men from the people of the East came to the Prophet, may God bless him and grant him peace, and they delivered speeches. The people were amazed by their eloquence. The Messenger of God, may God bless him and grant him peace, said: "Indeed, some eloquence is magic," or: "Indeed, part of eloquence is magic."