It is narrated from Ziyad bin Jubair, he says: I saw a man who came to Sayyiduna Abdullah bin Umar (may Allah be pleased with him) and said: I have vowed to fast every Wednesday, and now this day has fallen on Eid al-Adha or Eid al-Fitr, so what should I do? Sayyiduna Ibn Umar (may Allah be pleased with them both) said: Allah Almighty has commanded the fulfillment of vows, but the Messenger of Allah (peace and blessings be upon him) has forbidden fasting on the day of sacrifice (i.e., the tenth of Dhul-Hijjah).