Sahih Muslim Book 6, Hadith Number 2482.

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

Humaid reported that Anas (Allah be pleased with him) was asked about fasting during Ramadan while travelling. He said: We travelled with the Messenger of Allah (may peace be upon him) during the month of Ramadan, but neither the observer of the fast found fault with the breaker of the fast, nor the breaker of the fast found fault with the observer of the fast.