It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) prescribed this method: one camel may be slaughtered on behalf of seven people, and likewise, one cow may be slaughtered on behalf of seven people.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14593
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف لضعف مجالد بن سعيد، وانظر: 14116 و 14127