Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.007B.
Section : Reports concerning four rak’at.
Ibn ‘Umar said: “We observed and preserved from the Prophet ten rak’at [of sunnah prayers]: two before zuhr and two after it, two after maghrib in his house, two after ‘isha in his house and two rak’at before the fajr.” This is related by al-Bukhari.
Al-Mughirah ibn Sulaiman reports that he heard Ibn ‘Umar say: “The Prophet never left the two rak’at before zuhr and two rak’at after it, two rak’at after maghrib, two rak’a~ after ‘isha and two rak’at before fajr.” This is related by Ahmad with a good chain.