When is it best to start congratulating each other for Eid?
It should be on the day of eid after the prayer as it comes in some narrations
بإسناد حسن عن جبير بن نفير قال ” كان أصحاب رسول الله – صلى الله عليه وسلم – إذا التقوا يوم العيد يقول بعضهم لبعض : تقبل الله منا ومنك
Hafidh Ibn Hajr rahimahullah said:
“With a Hasan chain from Jubair ibn Nufayr said: The Companions of the Messenger sallahu alayhi wa salam if they used to met on the day of eid they would say to one another: May Allah accept from you and me”
Shaikhul Islaam Ibn Taymiyyah rahimahullah was asked:
Is the greeting on Eid and what the people say: Eid Mubarak and what resembles that legislated or not? If it does have an origin in the legislation, then what is said? Please give us a verdict may Allah reward you.
As for the greeting on Eid, each person says to the other when meeting after the Eid prayer: Tabbaqal Allah Minna wa Minkum and Wa Ahalahul Allahu Alayka and what resembles that. This has been reported from a group of the Companions radiallahu anhu and they allowed it. However, Imam Ahmed said: I do not initiate it to anyone. If someone initiates it with me then I respond to it. That is because responding is obligatory. As for initiating the greeting then it is not a Sunnah ordered. It is also not something prohibited. So whoever does it, then he has an example and whoever leaves it off, then he has an example. And Allah Knows Best”
[Majmoo’ al-Fatawa (24/253)]
Faisal Ibn Abdul Qaadir Ibn Hassan