Musnad Ahmad 27:1026

Yazid narrated to us, Yahya ibn Sa'id informed us, from Nafi', that he heard Ibn 'Umar narrating about that which the Messenger of Allah (peace and blessings of Allah be upon him) used to recite for the Talbiyah, saying: "Labbayk Allahumma Labbayk, Labbayka la sharika laka Labbayk, inna al-hamda wa an-ni'mata laka wa al-mulk, la sharika lak." And Nafi' mentioned that Ibn 'Umar used to add these words of his own: "Labbayk wa ar-raghba'u ilayk, wa al-'amalu Labbayk Labbayk."