Assalaamu alaykum. Can we say that praying in the field where a Tablighi Ijtema is held every year (in Bangladesh) is worth 490 million good deeds?
All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
Saying that the reward of praying in that field is multiplied to such and such number of good deeds is a lie against Allah and His Prophet .
This is like the saying of the innovators who say that the reward is doubled in some places which they consider as sacred, while the Shariah did not give them any preference.
The multiplication of the reward at a particular place is something that cannot not be known except by revelation, as in the multiplication of reward for prayer in Al-Masjid Al-Haraam in Makkah and in the Prophet’s mosque in Madeenah and the Al-Aqsa mosque in Jerusalem.
However, there is no doubt that the greater the congregation is, the greater the reward of the prayer is.
Ubayy ibn Ka'b, may Allah be pleased with him, narrated that the Prophet said, “A man's prayer along with another man is better (in reward) than his prayer alone; and his prayer with two men is better than his prayer with one single man, and if there are more, then it is more pleasing to Allah, the Almighty…” [Ahmad, Abu Daawood, and An-Nassaa'i - Al-Albaani and Al-Arna'oot classified it as Hasan (good)]
Ash-Shawkaani said in Nayl Al-Awtaar about the interpretation of the above hadeeth, “This is evidence that if the congregation is greater, then this is better.”
Ash-Shawkaani also said in Ad-Daraari Al-Mudhiyyah Sharh Ad-Durar Al-Bahiyyah, “With regard to the abundance of reward when the congregation is greater, then this is confirmed in the narration from Ubayy ibn Ka’b.” Then he mentioned the wording of the above hadeeth.
Allah knows best.
You can search for fatwa through many choices