The Rites of Hajj (Kitab Al-Manasik Wa'l-Hajj)
Dawud :: Book 10 : Hadith 1760
Narrated Ali ibn AbuTalib:
When the Apostle of Allah (peace_be_upon_him) sacrificed the camels, he sacrificed thirty of them with his own hand, and then commanded me (to sacrifice them), so I sacrificed the rest of them.