Sahih Muslim Book 7, Hadith Number 3031.

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

Jabir b. ‘Abdullah (Allah be pleased with them) reported that Allah’s Messenger (may peace be upon him) sacrificed (animals) on behalf of his wives, and in the Hadith transmitted by Ibn Abu Bakr (the words are): “A cow on behalf of ‘Aisha on the occasion of the Hajj.”