Musnad Ahmad 939:6

Waki' narrated to us, Sufyan narrated to us, from Abdullah ibn Abi Labid, from al-Muttalib ibn Abdullah ibn Hantab, from Khallad ibn al-Sa'ib, from Zayd ibn Khalid al-Juhani, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Gabriel came to me and said: 'O Muhammad, command your companions to raise their voices with the Talbiyah, for it is among the rituals of Hajj.'"