Musnad Ahmad 27:33

Isma'il narrated to us, Ayyub narrated to us, from Nafi', that his son 'Abdullah ibn 'Abdullah entered upon Ibn 'Umar while he was in the house, and he said: "I do not feel secure that there will not be fighting among the people this year, so you will be prevented from reaching the House (the Ka'bah). If only you would stay?" He said: "The Messenger of Allah (ﷺ) went out, and the disbelievers of Quraysh stood between him and the House. If they stand between me and it, I will do as the Messenger of Allah (ﷺ) did." He said: "{There has certainly been for you in the Messenger of Allah an excellent pattern} [Al-Ahzab: 21]." He said: "I have already made an 'Umrah obligatory (upon myself)." Then he traveled until, when he was at Al-Bayda', he said: "I do not see their matter (Hajj and 'Umrah) as anything but one. I call you to witness that I have made Hajj obligatory along with my 'Umrah." Then he arrived and performed one Tawaf for both of them.