(12) باب مَنْ تَطَوَّعَ فِي السَّفَرِ فِي غَيْرِ دُبُرِ الصَّلَوَاتِ وَقَبْلَهَا
Narrated Salim bin `Abdullah:
Ibn `Umar said, "Allah's Messenger (ﷺ) used to pray the Nawafil on the back of his Mount (carriage) by signs facing any direction." Ibn `Umar used to do the same.
Reference: Sahih al-Bukhari 1105
In-book reference: Book 18, Hadith 25
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 20, Hadith 208