Musannaf Ibn Abi Shaybah 12565 — A man who vows to fast a day

Ziyad bin Jubayr said: A man came to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) and asked: A man vowed to fast one day, and that day turned out to be Eid al-Fitr or Eid al-Adha? Sayyiduna Ibn Umar (may Allah be pleased with them both) said: Allah Almighty has commanded the fulfilment of vows, and the Prophet (peace and blessings be upon him) forbade fasting on these days.