From Sahih Muslim (Hadith 3189):
Jabir b. 'Abdullah (Allah be pleased with them), describing the Hajj of Allah's Apostle (ﷺ) 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)
Reference: Muslim 3189