Musnad Ahmad 2:83

Sufyan narrated to us, from al-Zuhri, from Ubayd Allah ibn Abd Allah ibn Utbah, from Ibn Abbas, from Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not exaggerate in praising me as the Christians exaggerated in praising the son of Maryam, for I am only a servant. So say: 'His servant and His Messenger.'"