Digha Nikaya 1:1017
SUJATOAtha kho bhagavā dakkhiṇena passena sīhaseyyaṁ kappesi pāde pādaṁ accādhāya sato sampajāno uṭṭhānasaññaṁ manasikaritvā.
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, and focused on the time of getting up.