Sahih Muslim
The Book of Pilgrimage (Kitab Al-Hajj)
Book Number: 007 / Hadith Number: 3032
Ziyad b. Jubair reported that Ibn 'Umar came upon a person who was slaughtering (sacrificing) his camel and had made him kneel down. So he told him to make it stand up festered (and then sacrifice it) according to the Sunnah of the Holy Prophet (may peace be upon him).