Musnad Ahmad 32:1862

Ya'mar ibn Bishr narrated to us, Abdullah narrated to us, Humayd al-Tawil informed us, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) drove many sacrificial camels, and he said: "Labbayk for an 'Umrah and a Hajj." And I was at the side of the left thigh of his she-camel.