Musnad Abu Ya'la al-Mawsili 109:35

Zakariya ibn Yahya narrated to us, Hushaym narrated to us, from Abd al-Malik, who said: I heard Ata narrating from Jabir, who said: We used to perform Tamattu’ with the Messenger of Allah, may Allah bless him and grant him peace, and we would slaughter a cow on behalf of seven people, and we would share in it.