The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1794
Narrated Umar ibn al-Khattab:
As-Subayy ibn Ma'bad said: I raised my voice in talbiyah for both of them (i.e. umrah and hajj). Thereupon Umar said: You were guided to the practice (sunnah) of your Prophet (peace_be_upon_him).