From Sahih Muslim (Hadith 2626):
A'isha (Allah be pleased with her) reported that Hamza b. Amr al-Aslami asked the Messenger of Allah (ﷺ) thus:Messenger of Allah, I am a person devoted much to fasting. Should I fast during the journey? He (the Holy Prophet) said: Fast if you like and break it if you like
Reference: Muslim 2626