The Messenger of Allah (may Allah's peace and blessings be upon him) used to offer voluntary prayer on the back of his riding beast (camel), whatever direction it went. He would nod his head. Ibn ‘Umar would do so as well

Explanation

The Messenger of Allah (may Allah's peace and blessings be upon him) used to perform the voluntary prayer only on the back of his riding beast, regardless of its direction. He would gesture with his head instead of bowing and prostration and did not bother to dismount to bow, prostrate himself, or face the Qiblah. This applies equally to the voluntary prayers, the regular Sunnah prayers, and other prayers fir specific reasons. The Prophet (may Allah's peace and blessings be upon him) however, did not do so when performing the obligatory prayers. In addition, he would offer the Witr prayer on the back of his camel.