Sahih Muslim Book 6, Hadith Number 2471.

Chapter : Permissibility of observing the fast or not observing it in the month of Ramadan for a traveller.

Ibn Abbas (Allah be pleased with him) reported: Do not condemn one who observes fast, or one who does not observe (in a journey) for the Messenger of Allah (may peace be upon him) observed fast in a journey or he did not observe it (too).