Rasulullah (sallallahu alayhi wasallam) said:

"All (lawful and necessary) expenditure is in the Path of Allah except building (expenditure), for there is no goodness in it."

Building expenditure refers to unnecessary building structures which people erect because of pride and show. The expensive Musjids and Daarul Uloom buildings constructed at huge costs in places where there is no need for these structures come within the scope of the prohibition and criticism of this Hadith.