Mu'awiyah bin Qurrah al-Muzani (may Allah have mercy on him) narrates that whenever Sayyiduna Ibn Abbas (may Allah be pleased with them both) was asked about sarf (the exchange of gold and silver), he would give a fatwa (permitting) it. At this, Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) spoke very harshly, so Sayyiduna Ibn Abbas (may Allah be pleased with them both) asked: "Who is this speaker?" The people said: "It is Sayyiduna Abu Sa'id (may Allah be pleased with him)." Then he said: "I did not think that anyone, knowing my kinship with the Messenger of Allah (peace and blessings be upon him), would confront me like this." Sayyiduna Abu Sa'id (may Allah be pleased with him) said: "I heard the Messenger of Allah (peace and blessings be upon him) forbidding it and declaring it unlawful." So after that, whenever Sayyiduna Ibn Abbas (may Allah be pleased with them both) was asked about it, he would say: "We met someone more knowledgeable than us; he informed us (of the Prophetic ruling), and we desisted (from our former position)."
Imam al-Tabarani (may Allah have mercy on him) said: "No one other than Sawadah (may Allah have mercy on him) narrated this hadith from Mu'awiyah bin Qurrah (may Allah have mercy on him), and Ya'qub (may Allah have mercy on him) is alone in narrating it."