The white days are present in every lunar month. It is the one in which the moon is in a full shape, from the beginning of the night to its end (they are the thirteenth, fourteenth and fifteenth). It is called white because of its whiteness at night by the moon and by day with the sun, and it was said because Allah forgave Adam in it and whitened his scroll.
The Kuwaiti Fiqh Encyclopedia defines the White Days as “the thirteenth day of the month, the fourteenth and the fifteenth of every Arab month. It was called white because of the whiteness of its nights with the moon; Because it is present from the beginning to the end of the night. Therefore, Ibn Berri said: It is correct to say: the days of the white nights, in addition to the fact that the whiteness is an attribute of the nights – that is, the days of the white nights. “
And regarding fasting on these days the Kuwaiti encyclopedia of jurisprudence said “and the white days are specialized with recommended fasting, narrated by Abu Dawood and Nisaai from Abdul Malik bin Milhan al-Qaisi, his father said: The Messenger of Allah (ﷺ) used to command us to fast the days of the white (nights): thirteenth, fourteenth and fifteenth of the month. He said: This is like keeping perpetual fast.
Sheikh Ibn Baz, may Allah have mercy on him, said: The white days are: the thirteenth, fourteenth, and fifteenth, these are the white days, meaning: whose night is white with the moon, and its day is white with the sun, its fasting is recommended, and if one fasts other days, there is nothing wrong, the Sunnah is for a Muslim to fast from Every month, three days, and this is for the Muslim woman too. The Messenger, peace and blessings be upon him, recommended fasting three days of every month. He told a group of companions, if they fast in the first ten days, or in the middle, or in the last, it is all good, and if they fast during the white days, it is better.
The Sheikh of the scholars of Algeria, Muhammad Sharef – may Allah have mercy on him – said about the white days: It is the gharar of every month, meaning the thirteenth, fourteenth and fifteenth. The name “Al-Gharar” is the plural of ghurah, and it is originally: the whiteness that is found in the forehead of a horse, because its nights are similar to the day in its whiteness because of the full moon completing its cycle. Malik, may Allah have mercy on him, disapproved of seeking to fast it, despite what came in the trail of encouraging to fast it, for fear that the ignorant would think that it is obligatory, and it was proven from him, peace and blessings of Allah be upon him, “that he used to fast three unspecified days every month.” Narrated by Muslim (2/ 818) [The Book of Fasting / Chapter: It is recommended to fast three days of every month], No. (1160/194).
And that he said to Abdullah bin Amr bin Al-Aas, may Allah be pleased with them, when he increased the fasting: “Isn’t it sufficient for you to fast three days a month?” I replied, “O Allah’s Apostle! (I can fast more).” He said, “Five?” I replied, “O Allah’s Messenger (ﷺ)! (I can fast more).” He said, “Seven?” I replied, “O Allah’s Messenger (ﷺ)! (I can fast more).” He said, “Nine (days per month)?” I replied, “O Allah’s Messenger (ﷺ)! (I can fast more)” He said, “Eleven (days per month)?” And then the Prophet said, “There is no fast superior to that of the Prophet (ﷺ) David it was for half of the year. So, fast on alternate days.” (Narrated by Al-Bukhari (4/264) [Book of Fasting / Chapter on the Fasting of David, peace be upon him]), No. 1980. And Muslim (2/817) [Book of Fasting / Chapter on the prohibition of fasting forever for those who are harmed by it…], No. 1159/191.
And it came in Al-Zarqani on Al-Mawahib that Ibn Abbas – may Allah be pleased with him – said: it was the custom of God’s messenger not to eat on the white days of the month whether travelling or not. narrated by Al-Nasa’i.
Also on the authority of Hafsa, she said: “There are four things which the Prophet never gave up: Fasting ‘Ashura‘, (fasting during) the ten days, (fasting) three days of each month, and praying two Rak’ahs before Al-Ghadah (Fajr).” Narrated by Ahmad.
It is also reported on the authority of Mu’adha al-‘Adawiya that she asked ‘A’isha whether God’s messenger used to fast three days every month, and she replied that he did. She asked which days in the month he fasted, and she replied that he did not care which days of the month he fasted. narrated by Muslim.
Then Al-Zarqani said: The wisdom in it is that it is in the middle of the month and the middle of anything is the most just. Also the eclipses of the moon – often happen in them, and it is commanded to increase in worship when it occurs. If the eclipse coincides with the one who is accustomed to fasting the white days, then he is prepared to combine different types of worship such as fasting, prayer and charity, unlike the one who doesn’t fast the white days, he will not be prepared for this.