(7) باب التَّطَوُّعِ فِي السَّفَرِ
Narrated Al-Bara' ibn Azib:
I accompanied the Messenger of Allah (ﷺ) on eighteen journeys and I never saw him fail to pray two rak'ahs when the sun had passed the meridian before offering the noon prayer.
Reference: Sunan Abi Dawud 1222
In-book reference: Book 4, Hadith 25
English translation: Book 4, Hadith 1218