أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، عَنْ شُعْبَةَ، قَالَ أَنْبَأَنَا أَنَسُ بْنُ سِيرِينَ، عَنْ رَجُلٍ، يُقَالُ لَهُ عَبْدُ الْمَلِكِ يُحَدِّثُ عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَأْمُرُ بِهَذِهِ الأَيَّامِ الثَّلاَثِ الْبِيضِ وَيَقُولُ " هُنَّ صِيَامُ الشَّهْرِ " .
It was narrated that a man called 'Abdul-Malik narrated from his father, that: the Messenger of Allah used to enjoin (fasting) these days of Al-Bid and he said: "That is (equivalent to) fasting for the whole month." Translation Not Available
Book Ref: Sunan An Nisai Book 22 Hadith 2430
Web Ref: Sunan An Nisai Vol 3 Book 22 Hadith 2432