It is narrated from Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Jibril (peace be upon him) came to me and said: 'Command your Companions to raise their voices in the talbiyah, for it is one of the rites of Hajj.'"
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5151