Sahih Muslim | Book 6 | Hadith Number 2474

Narrated by Jabir b. 'Abdullah (Allah be pleased with both of them)
Jabir b. 'Abdullah (Allah be pleased with both of them) reported that in the course of a journey Allah's Messenger (may peace be upon him) saw a man, people crowding around him and providing him a shade. Upon this he (the Holy Prophet) said: What is the matter with him? They said: He is a person observing fast. Whereupon the Messenger of Allah (may peace be upon him) said: It is no righteousness that you fast on journey.