Riyad Us-Saliheen (Gardens of the Righteous)
Undesirability of Eating in a Reclining Posture
746. Abu Juhaifah Wahb bin `Abdullah (May Allah be pleased with him) reported: Messenger of Allah (PBUH) said, "I do not eat reclining (against a pillow).''
Commentary: What is meant by reclining? There is a difference of opinion on it. Some say that it means leaning on one side, whether right or left, or against the wall. Imam Al-Khattabi takes it in this sense that somebody should lay out a mattress and sit on it comfortably as one sits cross-legged. Messenger of Allah (PBUH) used to take hardly an adequate meal. Ibn Hajar says that one should sit with the right knee drawn up and the left one bent down.
747. Anas (May Allah be pleased with him) reported: I saw Messenger of Allah (PBUH) eating some dates while sitting on his buttocks, with his legs raised.
Commentary: This Hadith sheds light on another sitting posture of Messenger of Allah (PBUH). But it betrays his uneasy state. In fact, when he was in a hurry he would be eager by eating a few dates so that he might be free to attend to some more important business. Also a report of Anas (May Allah be pleased with him) quoted by Muslim explains this state of mind of Messenger of Allah (PBUH).