Sunan al-Nasa'i The Book of Fasting Abu Ishaq al-Sabay'ai' أبو إسحاق السبيعي عمرو بن عبد الله Jarir bin 'Abdullah al-Bajli Mukhalad bin al-Hasan bin Abi Zamil مخلد بن الحسن بن أبي زميل Ubaidullah bin 'Umar bin Hafs عبيد الله بن عمر بن حفص بن عاصم Zayd bin Abi Anisa زيد بن أبي أنيسة “I entered upon the Mother of the Believers and heard her say: ‘The Messenger of Allah used to fast three days of each month: The first Monday of the month, then Thursday, then the following Thursday.” https://parallelquran.com/hadith/sunan-al-nasai-2420/