Sahih Muslim Book 4, Hadith Number 1524.

Chapter : Permissibility of combining two prayers on a journey.

‘Abdullah b. Shaqiq al-‘Uqaili reported: A person said to Ibn ‘Abbas (as he delayed the prayer): Prayer. He kept silence. He again said: Prayer. He again kept silence, and he again cried: Prayer. He again kept silence and said: May you be deprived of your mother, do you teach us about prayer? We used to combine two prayers during the life of the Messenger of Allah (may peace be upon him).