Mukhtasar Muslim

Sayyiduna Jabir (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings of Allah be upon him) sent me for some task. When I returned and reached him, he (peace be upon him) was riding (his mount). Qutaiba said that he (peace be upon him) was performing (nafl) prayer. I greeted him with salam, and he (peace be upon him) replied by gesture. When he finished the prayer, he called me and said, "You just greeted me with salam, and I was performing prayer (so I could not reply verbally)." Although his face was towards the east (and not towards the qiblah), (from this it is known that while performing nafl prayer on a mount, it is not necessary to face the qiblah).