Musnad Ahmad 32:2037

Yahya ibn Adam narrated to us, Sharik narrated to us, from Mansur, from Salim ibn Abi al-Ja'd, from Anas, who attributed it to the Prophet, may Allah bless him and grant him peace, that he combined the Umrah and the Hajj. He said: "Labbayk for a Hajj and an Umrah together."