Musnad Ahmad 5:145

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Yahya ibn 'Abbad ibn 'Abdullah ibn al-Zubayr narrated to me, from his father, from 'Abdullah ibn al-Zubayr, who said: By Allah, we were with 'Uthman ibn 'Affan at al-Juhfah, and with him was a group of the people of Syria, among them Habib ibn Maslamah al-Fihri. Then 'Uthman said—and the enjoyment of 'Umrah during Hajj was mentioned to him—: "Indeed, it is more complete for the Hajj and 'Umrah that they not be in the months of Hajj. If you were to delay this 'Umrah until you visit this House twice, it would be better, for Allah the Exalted has expanded the good." 'Ali ibn Abi Talib was in the bottom of the valley feeding a camel of his. It reached him what 'Uthman had said, so he came until he stood before 'Uthman and said: "Do you intend to restrict a Sunnah that the Messenger of Allah, peace and blessings of Allah be upon him, established, and a concession that Allah the Exalted granted to His servants in His Book, and forbid it? It was for those in need and those from distant lands." Then he entered into the state of Ihram for Hajj and 'Umrah together. 'Uthman turned to the people and said: "Did I forbid it? I did not forbid it. It was only an opinion I suggested; whoever wishes may take it, and whoever wishes may leave it."