(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. (PT)
Reference (PT): Sunan an-Nasa'i 2414 (PT)
In-book reference (PT): Book 22, Hadith 325 (PT)
English translation (PT): Vol. 3, Book 22, Hadith 2416 (PT)