Musannaf Ibn Abi Shayba 8:2436

Abu Bakr narrated to us, he said: Ibn Fudayl and Hafs narrated to us, from Yahya bin Sa'id, from 'Abd al-Rahman bin Abi Salamah, from Ibn 'Umar, he said: We set out early with the Messenger of Allah, may Allah bless him and grant him peace, from Mina to 'Arafat. Among us were those who were saying the takbir (Allahu Akbar), and among us were those who were saying the talbiyah (Labbayk Allahumma Labbayk).