Muhammad bin Abi Bakr bin Muhammad محمد بن أبي بكر بن محمد بن عمرو · The Chapters on Business Transactions

"I heard him meaning Ibn 'Abbas allowing exchange (of Dirhams for Dirham etc., if extra was given) and that was narrated from him. Then I heard that he has taken back this opinion. I met him in Makkah and said: 'I heard that you had taken back (your opinion).' He said: 'Yes. That was just my own opinion, but Abu Sa'eed narrated from the Messenger of Allah (ﷺ) that he forbade exchange (of like items if extra is given)."'