Question: What is the ruling on someone who observed Sawm (Fast) on the Two `Eeds?
Answer: It is not permissible to observe Sawm on the Two `Eeds; and anyone who does so is blameworthy. It is obligatory on them to make Tawbah (repentance to Allaah) for this sin. This is because Allaah (Exalted be He) has made these days for eating, drinking, and observing Thikr (Remembrance of Allaah). Therefore, whoever observes Sawm on these days disobeys Allaah (Exalted be He) and His Messenger (peace be upon him)… read more here.