Sunan an Nasai
2294
Sahih+2

It was narrated from Hamza bin 'Amr Al-Aslami that:he asked the Messenger of Allah about fasting while traveling. He said: "If," then he said something to the effect that: "If you want, then fast, and if you want, then do not fast

SahihAbu Ghuddah
SahihAl-Albani