Sahih Muslim The Book of Fasting Ziyad bin 'Abdullah زياد بن عبد الله بن الطفيل Sahih 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 (Allah be pleased with him) 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. https://parallelquran.com/hadith/sahih-muslim-2559/