It is narrated from Sayyiduna al-Sa'ib bin Khallad al-Ansari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Jibril (peace be upon him) came to me and commanded me to order my Companions, or those with me, to raise their voices with the talbiyah, or with the call of ihram, and he said: It is one of the rites of Hajj."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6596