Musnad Ahmad 27:698

Sahl ibn Yusuf narrated to us, from Humayd, from Bakr, who said: I said to Ibn Umar, "Indeed, Anas informed us that the Prophet, peace and blessings of Allah be upon him, said: 'Labbayk for an Umrah and a Hajj.'" He said, "And did Anas go out and recite the Talbiyah for Hajj, and we recited the Talbiyah with him? When he arrived, he commanded those who did not have the sacrificial animal with them to make it an Umrah." He said: So I mentioned that to Anas, and he said, "He does not consider us to be anything but children."