Trường Bộ Kinh (Digha Nikaya) 1:1059
SUJATOAtha kho bhagavā dakkhiṇena passena sīhaseyyaṁ kappesi pāde pādaṁ accādhāya sato sampajāno.
And then the Buddha laid down in the lion’s posture—on the right side, placing one foot on top of the other—mindful and aware.