Sayyidah Umm Habibah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever offers twelve voluntary rak'ahs besides the obligatory prayers, Allah Almighty will build a house for him in Paradise."
(b) Sayyidah Umm Habibah (may Allah be pleased with her) said that the Prophet (peace and blessings be upon him) said: "Whoever offers twelve voluntary rak'ahs in a day and night besides the obligatory prayers, Allah Almighty will build a house for him in Paradise." Sayyidah Umm Habibah (may Allah be pleased with her) said: After that I never left these twelve rak'ahs. Anbasah and Amr (may Allah have mercy on them) also said: We too never left these twelve rak'ahs. Al-Nu'man (may Allah have mercy on him) said: It is hardly possible that I would leave them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4479