Ata bin Abi Rabah says that once Abdullah bin Abbas (may Allah be pleased with them both) invited his brother, Sayyiduna Fadl (may Allah be pleased with him), to eat on the day of Arafah. He replied that he was fasting. Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Do not fast on this day (in the state of Ihram), because milk was milked and presented to the Prophet (peace and blessings be upon him) in a vessel on this day, and the Prophet (peace and blessings be upon him) drank it. And people follow you (so seeing you fasting, they might start considering it important).