Musnad Abu Ya'la al-Mawsili 1:115

Ibrahim ibn Muhammad ibn ‘Ar‘arah al-Sami narrated to us, Muhammad ibn Abi Fudayk narrated to us, from al-Dahhak ibn ‘Uthman, from Muhammad ibn al-Munkadir, from ‘Abd al-Rahman ibn Yarbu‘, from Abu Bakr al-Siddiq, who said: The Messenger of Allah (may Allah bless him and grant him peace) was asked: "Which deed is best?" He said: "The *‘ajj* (raising the voice in the Talbiyah) and the *thajj* (the shedding of the blood of the sacrificial animals)."