Nafi' (may Allah have mercy on him) said: When al-Hajjaj came against Ibn al-Zubayr (may Allah be pleased with them both), and Ibn Umar (may Allah be pleased with them both) had intended to perform Hajj, his sons Salim and Abdullah said to him: It will make no difference if you do not perform Hajj this year; we fear that fighting will break out among the people and you will be prevented from reaching the House. He said: If I am prevented from reaching the House, I will do as we did with the Prophet (peace and blessings be upon him) when Quraysh came between him (peace and blessings be upon him) and the House: he (peace and blessings be upon him) shaved his head and returned. I make you witnesses that I have made Umrah binding upon myself. Then he went to the tree and said the talbiyah for Umrah, until, when he ascended al-Bayda', he said: The matter of both is one and the same; if I am prevented from Umrah, I am prevented from Hajj. Bear witness that I have made Hajj binding upon myself along with my Umrah. He (Nafi') said: At that time he had no sacrificial animal with him. He travelled on until he reached Qudayd, where he bought a sacrificial animal, garlanded it, marked it (ish'ar), and drove it along with him. When he entered Makkah, he performed one tawaf for both of them (Hajj and Umrah), of the House and of Safa and Marwah. He used to say: Whoever combines Hajj and Umrah, one tawaf suffices him. And he did not leave ihram until he had left ihram from both of them together.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9425