Sahih Al Bukhari Hadith Number 1000

Narrated Ibn `Umar: The Prophet (peace be upon him) used to offer (Nawafil) prayers on his Rahila (mount) facing its direction by signals, but not the compulsory prayer. He also used to pray witr on his (mount) Rahila.

14  Witr Prayer
Hadith number 1000
Volume no 2
Chapter: 6 (Offering prayers of Witr while on a journey)