Imam al-Sha'bi narrates: I asked Sayyiduna Abdullah bin Umar (may Allah be pleased with them both): Does one camel and one cow suffice on behalf of seven people? He said: "O Sha'bi! Would they be for seven people?" I said: The Companions of Muhammad (peace and blessings be upon him) say that the Prophet (peace and blessings be upon him) laid down the Sunnah that one camel is to be sacrificed on behalf of seven people and one cow on behalf of seven people. Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) asked a man: "O so-and-so! Is that so?" He replied: Yes. Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: "I was not aware of this."
Ahmad recorded it, and its narrators are the narrators of the "Sahih".
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الحج / 5390