Mukhtasar Bukhari (Abridged) 261 — Facing the qiblah wherever you are

Narrated Jabir (may Allah be pleased with him): The Prophet (peace and blessings of Allah be upon him) used to offer voluntary prayers on his mount, facing in whichever direction it turned. But when he intended to offer an obligatory prayer, he would dismount and face the Qiblah.