Musannaf Ibn Abi Shayba 13:2576

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Jabir, from ‘Amir; and from Sufyan, from Ibn Jurayj, from ‘Ata’: They both said: Pre-emption (al-shuf’ah) is according to the shares.