Musnad Ahmad 708:1

Qutaybah ibn Sa'id narrated to us, Ibn Lahi'ah narrated to us, from Zahrah ibn Ma'bad, from his grandfather, who said: We were with the Prophet, peace and blessings of Allah be upon him, and he was holding the hand of Umar ibn al-Khattab, may Allah be pleased with him. He said: "By Allah, O Messenger of Allah, you are more beloved to me than everything, except my own self." The Prophet, peace and blessings of Allah be upon him, said: "By the One in Whose hand is my soul, none of you shall believe until I am more beloved to him than his own self." Umar said: "Then, by Allah, you are now more beloved to me than my own self." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Now, O Umar."