Musnad Ahmad 27:349

Waki’ narrated to us, from Hisham ibn Sa’d, from ‘Umar ibn Usayd, from Ibn ‘Umar, who said: "We used to say during the time of the Prophet, may Allah bless him and grant him peace: 'The Messenger of Allah is the best of people, then Abu Bakr, then ‘Umar.'" And Ibn Abi Talib was given three characteristics; for me to have one of them is more beloved to me than red camels: The Messenger of Allah, may Allah bless him and grant him peace, married his daughter to him, and she bore him children; and he closed the doors [of the companions' houses] except his door in the mosque; and he gave him the banner on the day of Khaybar.