سورة At-Taubah ( The Repentance ) - الآية 108

Never stand (for worship) in that mosque*; indeed the mosque** that has been founded on piety from the very first day deserves that you should stand in it; in it are the people who wish to thoroughly cleanse themselves; and Allah loves the clean. (*The mosque built by the hypocrites. ** The mosque at Quba, built by the Holy Prophet and his companions. The merit of praying 2 Raka’ Nawafil in it is equal to the reward of an Umrah.)