Sunan an Nasai
2257
Sahih+2

It was narrated from Jabir bin 'Abdullah that:the Messenger of Allah saw some people gathered around a man, so he asked (what was happening) and they said: "It is a man who is exhausted because of fasting." The Messenger of Allah said: "It is not righteousness to fast when traveling

SahihAbu Ghuddah
SahihAl-Albani