From Sahih Muslim (Hadith 2629):
Hamza b. 'Amr al-Aslami (Allah be pleased with him) said:Messenger of Allah, I find strength in me for fasting on a journey; is there any sin upon me (in doing it)? Thereupon the Messenger of Allah (ﷺ) said: It is a concession from Allah. He who took advantage of it, it is good for him, and he who preferred to observe fast, there is no sin upon him. Harun (one of the narrators) in his narration said: 'lt is a concession, and he made no mention of" from Allah
Reference: Muslim 2629