Musnad Ahmad 1018:85

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, 'Umar ibn 'Abd Allah ibn 'Urwah ibn al-Zubayr narrated to me, from his grandfather 'Urwah, from whoever narrated to him from the companions of the Messenger of Allah, may Allah bless him and grant him peace, who said: "The Messenger of Allah, may Allah bless him and grant him peace, used to command us to build mosques in our houses, and to improve their construction and keep them clean."