Musannaf Ibn Abi Shayba 13:2801

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Ash’ath, from al-Hakam, who said: If the person entitled to pre-emption (al-shafi’) gives permission to the buyer to purchase, and he then purchases, there is no right of pre-emption for him.