رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 1262
The Book of Virtues
The Desirability of Observing Three Days of Fasting in Every Month
وَعَنْ أَبِي ذَرٍّ رَضِيَ اللَّه عَنْهُ، قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ: إِذَا صمت من الشهر ثلاثًا، فَصُمْ ثَلَاثَ عَشْرَةَ، وَأَرْبَعَ عَشْرَةَ وَخَمْسَ عَشْرَةَ رَوَاهُ التِّرْمِذِيّ وَقَالَ: حَدِيث حَسَن.
Abu Dharr (May Allah be pleased with him) reported: The Messenger of Allah (ﷺ) said, "If you want to observe Saum on three days in a month, then fast on the thirteenth, fourteenth and fifteenth of the (lunar) month." [At-Tirmidhi].
Riyad as-Salihin, 1262