Musnad Ahmad 27:622

He said: I found in my father’s book: Muhammad ibn Bakr narrated to us, Ibn Jurayj informed us, Nafi’ informed me, that Ibn ‘Umar used to say: I heard the Prophet, peace and blessings of Allah be upon him, saying: "Labbayk Allahumma Labbayk, Labbayka la sharika laka Labbayk, inna al-hamda wa an-ni’mata laka, wa al-mulka la sharika lak (Here I am, O Allah, here I am; here I am, You have no partner, here I am; indeed, all praise and grace are Yours, and the dominion; You have no partner)." Nafi’ said: And Ibn ‘Umar used to say: And I added: "Labbayk, Labbayka wa sa’dayk, wa al-khayru fi yadayk Labbayk, wa ar-raghba’u ilayka wa al-‘amal (Here I am, here I am and at Your service, and all good is in Your hands, here I am; and the longing is toward You, and the deed)."