Musnad Ahmad 32:1460

Yunus and Hassan ibn Musa narrated to us, they said: Hammad ibn Salamah narrated to us, from Ayyub al-Sakhtiyani, from Abu Qilabah, from Anas ibn Malik, that the Prophet, peace and blessings of Allah be upon him, said: "The Hour will not be established until people boast about the mosques."