Musannaf Ibn Abi Shayba 3:3602

Ghundar narrated to us, from Shu'bah, from Mansur, from Abu 'Uthman, the freed slave of Al-Mughirah ibn Shu'bah, from Abu Hurayrah, who said: "There is no Muslim servant who prays twelve rak'ahs in a day, except that Allah builds a house for him in Paradise."