Musnad Ahmad 1159:23

Bahz and Ibn Ja'far narrated to us, they said: Shu'bah narrated to us, from al-Nu'man ibn Salim, he said: I heard 'Amr ibn Aws narrating from 'Anbasah, from Umm Habibah, she said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no Muslim servant who performs ablution and perfects the ablution, then prays to Allah the Almighty every day twelve rak'ahs, but a house will be built for him in Paradise." Umm Habibah said: "I have not ceased praying them since." And 'Anbasah said: "I have not ceased praying them since." And 'Amr ibn Aws said: "I have not ceased praying them." Al-Nu'man said: "And I hardly ever leave them." Ibn Ja'far said: From 'Anbasah ibn Abi Sufyan, from Umm Habibah, the wife of the Prophet (peace and blessings of Allah be upon him), that she heard the Prophet (peace and blessings of Allah be upon him) saying: "There is no Muslim servant who prays to Allah the Almighty every day twelve rak'ahs voluntarily, other than the obligatory ones," and he mentioned the like of it.