Musannaf Ibn Abi Shayba 3:3600

Abu Mu'awiyah narrated to us, from Isma'il bin Abi Khalid, from al-Musayyab bin Rafi', from 'Anbasah bin Abi Sufyan, from Umm Habibah bint Abi Sufyan—and she did not attribute it to the Prophet (marfu')—she said: "Whoever prays twelve rak'ahs in a day, other than the obligatory ones, a house will be built for him in Paradise."