مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2971
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The Messenger of Allah (ﷺ) travelled in Ramadan during the year of the conquest. He fasted until he reached 'Usfan, then he called for a vessel and drank during the day so that the people would see him. Then he did not fast until he entered Makkah, and he conquered Makkah in Ramadan. Ibn 'Abbas said: So the Messenger of Allah (ﷺ) fasted whilst travelling and did not fast. So whoever wants to may fast and whoever wants to may not fast.
Musnad Ahmad 2994its isnad is saheeh, al-Bukhari (4279) and Muslim (1113)]