Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) was asked which deed is best, and he (peace and blessings be upon him) said: "Al-'ajj and al-thajj (raising the voice in the talbiyah and pouring forth the blood of sacrificial animals)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9016