The best is to fast them on the White Days, which are the thirteenth, the fourteenth, and the fifteenth. It is also said: the twelfth, the thirteenth, and the fourteenth. But the correct and well-known view is the first.
رياض الصالحينAbū Zakariyyā Muḥyī al-Dīn Yaḥyā ibn Sharaf al-Nawawī٢٣٠ - باب استحباب صوم ثلاثة أيام من كل شهر
٢٣٠ - باب استحباب صوم ثلاثة أيام من كل شهر
- ﵁ - - ﷺ -
On the authority of Abū Hurayra (may Allah be pleased with him), who said: My intimate friend ﷺ enjoined upon me three things: fasting three days of every month, the two rakʿahs of the forenoon prayer (ḍuḥā), and that I perform the witr prayer before I sleep. Agreed upon.
- ﵁ - - ﷺ -
On the authority of Abū al-Dardāʾ (may Allah be pleased with him), who said: My beloved ﷺ enjoined upon me three things which I will never abandon as long as I live: fasting three days of every month, the forenoon prayer (ḍuḥā), and that I do not sleep until I have performed the witr prayer. Narrated by Muslim.
وعن عبد الله بن عمرو بن العاص ﵄، قَالَ: قَالَ رسول الله - ﷺ: «صَوْمُ ثَلاَثَةِ أيَّامٍ مِنْ كُلِّ شَهْرٍ صَوْمُ الدَّهْرِ كُلِّهِ». متفقٌ عَلَيْهِ.
On the authority of ʿAbd Allāh ibn ʿAmr ibn al-ʿĀṣ (may Allah be pleased with them both), who said: The Messenger of Allah ﷺ said: "Fasting three days of every month is like fasting the whole of time." Agreed upon.
وعن مُعاذة العدوية: أنها سألت عائشةَ ﵂: أكَانَ رسول الله - ﷺ - يَصُومُ مِنْ كُلِّ شَهْرٍ ثَلاَثة أيَّامٍ؟ قالت: نَعَمْ. فقلتُ: مِنْ أيِّ الشَّهْرِ كَانَ يَصُومُ؟ قالت: لَمْ يَكُنْ يُبَالِي مِنْ أيِّ الشَّهْرِ يَصُومُ. رواه مسلم.
On the authority of Muʿādha al-ʿAdawiyya, that she asked ʿĀʾisha (may Allah be pleased with her): Did the Messenger of Allah ﷺ fast three days of every month? She said: Yes. I said: From which part of the month did he fast? She said: He did not mind from which part of the month he fasted. Narrated by Muslim.
وعن أَبي ذر - ﵁ - قَالَ: قَالَ رسول الله - ﷺ: «إِذَا صُمْتَ مِنَ الشَّهْرِ ثَلاَثًا، فَصُمْ ثَلاَثَ عَشْرَةَ، وَأرْبَعَ عَشْرَةَ، وَخَمْسَ عَشْرَةَ». رواه الترمذي، وقال: «حديث حسن».
On the authority of Abū Dharr (may Allah be pleased with him), who said: The Messenger of Allah ﷺ said: "When you fast three days of the month, then fast the thirteenth, the fourteenth, and the fifteenth." Narrated by al-Tirmidhī, who said: "A good (ḥasan) hadith."
وعن قتادة بن مِلْحَان - ﵁ - قَالَ: كَانَ رسولُ الله - ﷺ - يَأمُرُنَا بِصِيَامِ أيَّامِ البِيضِ: ثَلاثَ عَشْرَةَ، وَأرْبَعَ عَشْرَةَ، وَخَمْسَ عَشْرَةَ. رواه أَبُو داود.
On the authority of Qatāda ibn Milḥān (may Allah be pleased with him), who said: The Messenger of Allah ﷺ used to command us to fast the White Days: the thirteenth, the fourteenth, and the fifteenth. Narrated by Abū Dāwūd.
وعن ابن عباس ﵄، قَالَ: كَانَ رسولُ اللهِ - ﷺ - لاَ يُفْطِرُ أيَّامَ البِيضِ في حَضَرٍ وَلاَ سَفَرٍ. رواه النسائي بإسنادٍ حسن .
On the authority of Ibn ʿAbbās (may Allah be pleased with them both), who said: The Messenger of Allah ﷺ would not omit fasting the White Days, whether resident or travelling. Narrated by al-Nasāʾī with a good (ḥasan) chain.