Sahih Muslim Book 7, Hadith Number 3028.

Chapter : It is permissible to join seven persons in a cow or a camel.

Jabir b. ‘Abdullah (Allah be pleased with them), describing the Hajj of Allah’s Apostle (may peace be upon him) said: He (the Holy Prophet) commanded us as we had entered into the state of Ihram to sacrifice the animals (as a rite of Hajj) and a group (of person; amongst us, i.e. seven) shared in the sacrifice of one (camel or cow), and it happened at that time when he commanded them to put off Ihram for Hajj (after performing ‘Umra).