When I came to the Prophet (ﷺ) in his house, I saw him sitting reclining on a pillow. The narrator Ibn al-Jarrah added: "on his left side".

Abu Dawud said: Ishaq b. Mansur transmitted it from Isra'il, also mentioning the words "on his left side".
Sunan Abi Dawud Book 34, Hadith 124