Musnad Abu Ya'la al-Mawsili 154:10

Bishr ibn al-Walid al-Kindi narrated to us, [saying] Abd al-Aziz ibn Muhammad al-Darawardi narrated to us, from Zayd ibn Aslam, from Ibn Umar: That two men arrived during the time of the Messenger of Allah, may Allah bless him and grant him peace, and they delivered a speech. The people were amazed by their speech. The Messenger of Allah, may Allah bless him and grant him peace, turned to us and said: "Indeed, some eloquence is magic," or "Indeed, part of eloquence is magic."