Musnad Ahmad 1159:11

Yazid ibn Harun narrated to us, he said: Isma'il ibn Abi Khalid narrated to us, from al-Musayyib ibn Rafi', from 'Anbasah ibn Abi Sufyan, from Umm Habibah bint Abi Sufyan, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever prays twelve prostrations in a day and a night, other than the obligatory ones, a house will be built for him in Paradise."