Question
Out of the 3 white days which of them is considered to be when the moon is at its fullest (100%)? Is there any evidence to support this ?
Answer:
ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﯿﻢ
In the name of Allah, the Most Gracious, the Most Merciful
The Messenger (s.a.w.) said, “O Abu Dhar! When you fast three days out of a month, then fast the thirteenth, fourteenth, and fifteenth.” (Tirmizi: 761) These three days are called the “white days” (*Ayaamul Beedh*) because the nights become white (i.e. radiant) due to the visibility of the moon from the 13th until the 15th. (Al-Mawsoo’ah Al-Fiqhiyyah Al-Kuwaytia: v. 7, p. 319 [Wizarat Al-Awqaf wa Al-Shuoon Al-Islamia Al-Kuwait])
As for the question-- in which of these nights is the moon the fullest, I have not come across any evidence for that neither from the Quran nor Sunnah. Therefore, it is advised that you consult an astronomer regarding this issue.
Only Allah knows best
Written by Maulana Mohammad Ahsan Osmani Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham