Musnad Ahmad 27:575

Muhammad ibn Ja'far narrated to us, Sa'id narrated to us, from Qatadah, from Bakr ibn 'Abdullah, from Ibn 'Umar, that he said: The Talbiyah of the Messenger of Allah, peace and blessings of Allah be upon him, was: "Labbayk Allahumma Labbayk, Labbayka la sharika laka Labbayk, inna al-hamda wa an-ni'mata laka wa al-mulk, la sharika lak." (At Your service, O Allah, at Your service; at Your service, You have no partner, at Your service; indeed, all praise and grace are Yours, and the dominion; You have no partner.)