(17) باب التَّخْيِيرِ فِي الصَّوْمِ وَالْفِطْرِ فِي السَّفَرِ
'A'isha (Allah be pleased with her) reported that Hamza b. 'Amr al-Aslami asked the Messenger of Allah (ﷺ) about fasting on a journey, and he (the Holy Prophet) said:
Fast if you like and break it if you like.
Reference: Sahih Muslim 1121 a
In-book reference: Book 13, Hadith 131
USC-MSA web (English) reference(deprecated numbering scheme): Book 6, Hadith 2487