Sahih Muslim Book 4, Hadith Number 1521.

Chapter : Permissibility of combining two prayers on a journey.

Ibn ‘Abbas reported: I observed with the Apostle of Allah (may peace be upon him) eight (rak’ahs) in combination, and seven rak’ahs in combination. I (one of the narrators) said: O Abd Sha’tha’, I think that he (the Holy Prophet) had delayed the noon prayer and hastened the afternoon prayer, and he delayed the sunset prayer and hastened the ‘Isha prayer. He said: I also think so.