Musannaf Ibn Abi Shayba 3:3598

Abu Bakr narrated to us, he said: Ishaq bin Sulayman narrated to us, from Mughira bin Ziyad, from Ata, from Aisha, she said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever persists in twelve rak'ahs of the Sunnah, Allah will build for him a house in Paradise: four before the Dhuhr, two after it, two after the Maghrib, two after the Isha, and two before the Fajr."