Q- Is the following a Hadith?“A believer in the Masjid is like a fish in the water and a hypocrite in the Masjid is like a bird in the cage”
Allamah ‘Ajluni (rahimahullah) states that although this is famously [quoted] as a Hadith, he does not know of these words to be a Hadith. He further states that this seems to be the statement of Malik ibn Dinar (rahimahullah). (Kashful Khafa, Hadith: 2689)
This should therefore not be quoted as a Hadith of Nabi (sallallahu ‘alayhi wa sallam), despite its meaning being correct.
And Allah Ta’ala Knows best.
https://hadithanswers.com/a-believer-in-the-masjid-is-like-a-fish-in-water/