Musnad Ahmad 28:578

'Affan narrated to us, 'Abd al-Wahid ibn Ziyad narrated to us, from al-Hajjaj, from 'Amr ibn Shu'ayb, from his father, from his grandfather, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever builds a mosque for Allah, a house wider than it is built for him in Paradise."