Sunan an Nasai
2300
Sahih+2

It was narrated that Hamzah bin 'Amr said:"I used to fast continually at the time of the Messenger of Allah. I said: 'O continually while traveling.' He said: 'If you wish then fast, and if you wish then do not fast

SahihAbu Ghuddah
SahihAl-Albani