Muwatta 1262

Malik says of a group who all hunt game while in ihram or in the sanctuary: each one of them owes its penalty; if they are judged an offering, each owes an offering; if fasting, each owes fasting. Likewise a group who kill a man by mistake: the expiation is freeing a slave for each of them, or two consecutive months of fasting for each of them. ¹

Belongs to the Muwatta, Book of Pilgrimage (hajj). Source: the Muwatta. Built on in the chapters on expiation (kaffara), the offering (hady) and fasting (sawm).