Musnad Abu Ya'la al-Mawsili 113:27

'Uqbah ibn Mukram narrated to us, Yunus ibn Bukayr narrated to us, Salih ibn Rustum narrated to us, from Abu Qilabah, from Anas ibn Malik, who said: We went out with him toward the Haram, and the time for prayer arrived. He said, "Will you not descend so that we may pray?" I said, "If you would proceed to this mosque." He said, "Which mosque?" It was said, "The mosque of the sons of so-and-so." He became alarmed and said: I heard him—meaning the Prophet (peace and blessings of Allah be upon him)—saying: "A time will come upon my Ummah when they will boast about mosques, and they will not populate them except for a few."