Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.115B.

The scholars are in agreement that one is to combine the zuhr and ‘asr prayer during the time of the zuhr prayer, at ‘Arafa [during the performance of the pilgrimage], and the maghrib and ‘isha prayers during the time of the ‘isha at muzdalifah, following the example of the Prophet.