Musnad Ahmad 27:1250

Rawh narrated to us, Salih ibn Abi al-Akhdar narrated to us, Ibn Shihab narrated to us, from Salim, who said: Abdullah ibn Umar used to issue legal opinions based on what Allah, the Almighty and Majestic, revealed regarding the concession of *Tamattu’* (combining Hajj and Umrah), and what the Messenger of Allah, peace and blessings of Allah be upon him, practiced regarding it. Some people would say to Ibn Umar: "How can you oppose your father when he forbade that?" Abdullah would say to them: "Woe to you! Do you not fear Allah? If Umar forbade that, he was seeking goodness in it, desiring by it the completion of the Umrah. So why do you forbid that which Allah has permitted and the Messenger of Allah, peace and blessings of Allah be upon him, practiced?" "Is the Messenger of Allah, peace and blessings of Allah be upon him, more worthy for you to follow his Sunnah, or the Sunnah of Umar? Indeed, Umar did not say to you that Umrah during the months of Hajj is forbidden, but he said: 'The completion of the Umrah is that you separate it from the months of Hajj.'"