Musannaf Ibn Abi Shayba 13:695

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from Abu al-Haytham, he said: I heard Ibrahim and al-Sha’bi discussing that. Ibrahim said: "It is not permissible." Al-Sha’bi said: "Why?" Ibrahim said: "Because you do not know whether he has repented or has not repented."