The White Days (Ayyam al-Bid, literally “the bright days”) are the 13th, 14th, and 15th of every Hijri month – the three nights when the moon is at or very near full. The name reflects the brightness of the night sky on these dates: in a lunar calendar synchronized to actual moon sightings, the middle of the month is always the time of the full moon, making these dates astronomically consistent across all twelve months. They form one of the most regular and widely observed voluntary fasts in the Sunni tradition.

The basis for the practice is the direct instruction of the Prophet Muhammad (peace be upon him), recorded in multiple authentic narrations. In Jami at-Tirmidhi 761, Abu Dharr (may Allah be pleased with him) reported: “The Messenger of Allah, peace be upon him, said to me: ‘When you fast three days out of a month, then fast the thirteenth, fourteenth, and fifteenth.'” A parallel narration in Sunan an-Nasai 2425 preserves the same instruction.

The Prophet (peace be upon him) also gave a general recommendation to fast three days of every month, which the White Days fulfill in a fixed, easy-to-remember way. Abu Hurairah (may Allah be pleased with him) reported in Sahih al-Bukhari 1910: “My friend (the Prophet (ﷺ) ) advised me to observe three things: (1) to fast three days a month; (2) to pray two rak`at of Duha prayer (forenoon prayer); and (3) to pray witr before sleeping.” The reward for these three days is described in Jami at-Tirmidhi 762 as equivalent to fasting the entire month, since every good deed is multiplied by ten.

The White Days are observed in the same way as any voluntary day fast, with abstention from food, drink, and marital relations from dawn until sunset. If a White Day coincides with a day on which fasting is prohibited – specifically the Days of Tashriq, which are 13, 14, and 15 of Dhul-Hijjah – the fast is not observed on those days. In all other months, the three days fall in the heart of the month, far from any prohibited dates.

For more details on the individual observance, see the calendar entry for the White Days, which appears on the calendar grid for every Hijri month.