Musnad Abu Ya'la al-Mawsili 153:37

Abu Khaythama narrated to us, Ya'qub ibn Ibrahim narrated to us, my father narrated to us, from Ibn Ishaq, who said: Muhammad ibn Muslim narrated to me, from Salim ibn Abdullah ibn Umar, who said: A man from the people of Syria sat with Abdullah ibn Umar, and I was with him. He said to him, "O Abu Abd al-Rahman, what is your view on performing Tamattu' (combining) Umrah with Hajj?" Abdullah said to him, "It is good and beautiful for whoever does that." The man said, "But your father used to forbid it." Abdullah became angry and then said, "Woe to you! Tell me, if my father forbade it, but the Messenger of Allah (may Allah bless him and grant him peace) practiced it, should you follow the command of the Messenger of Allah (may Allah bless him and grant him peace) or the command of my father?" He said, "Nay, rather the command of the Messenger of Allah." He said, "For the Messenger of Allah (may Allah bless him and grant him peace) indeed did that, so get up and go about your business."