(83) باب كَيْفَ يَصُومُ ثَلاَثَةَ أَيَّامٍ مِنْ كُلِّ شَهْرٍ وَذِكْرِ اخْتِلاَفِ النَّاقِلِينَ لِلْخَبَرِ فِي ذَلِكَ .
It was narrated from Ibn 'Umar that:
the Messenger of Allah used to fast three days of each month: Monday at the beginning of the month, the following Thursday, then the Thursday after that. (ID)
Reference (ID): Sunan an-Nasa'i 2414 (ID)
In-book reference (ID): Book 22, Hadith 325 (ID)
English translation (ID): Vol. 3, Book 22, Hadith 2416 (ID)