Anas bin Sirin (may Allah have mercy on him) says that when Hazrat Anas (may Allah be pleased with him) returned from Syria, we met him; we encountered him at a place called ‘Ain al-Qamar. At that time, he was performing prayer on his mount without facing the Qiblah. We said to him, “Are you performing prayer without facing the Qiblah?” He replied, “If I had not seen the Prophet (peace and blessings be upon him) doing so (in voluntary prayers), I would not have done so (in voluntary prayers) either.”
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 13113