Ziyad bin Jubair reported that a person came to Ibn Umar (RA) and said: I had taken a vow that I would fast on the day (but it accidentally) synchronises with the day of Adha or the day of Fitr. Thereupon Ibn Umar (RA) said: Allah, the Exalted, has commanded fulfilling of the vow, but the Messenger of Allah ﷺ has forbidden the observance of fast on this day.