Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.008.
Section : Reports concerning six rak’at.
‘Abdullah ibn Shaqiq said: “I asked ‘Aishah about the prayer of the Prophet and she said: ‘He would pray four rak’at before zuhr and two after it.”‘ This is related by Ahmad, Muslim, and others.
Umm Habibah bint Abu Sufyan reports that the Messenger of Allah said: “Whoever prays twelve rak’at during the day and night will have a house built for him in paradise: four rak’at before zuhr and two after it, two rak’at after maghrib, two rak’at after ‘isha, and two rak’at before fajr.” This is related by at-Tirmizhi who called it hasan sahih. Muslim reports it briefly.