Sahih al-Bukhari, Volume 7, Book 65, Hadith 311 (USC-MSA) ⓘ
Narrated Abu Juhaifa: While I was with the Prophet he said to a man who was with him, "I do not take my meals while leaning."
حَدَّثَنِي عُثْمَانُ بْنُ أَبِي شَيْبَةَ، أَخْبَرَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ عَلِيِّ بْنِ الأَقْمَرِ، عَنْ أَبِي جُحَيْفَةَ، قَالَ كُنْتُ عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَقَالَ لِرَجُلٍ عِنْدَهُ " لاَ آكُلُ وَأَنَا مُتَّكِئٌ " .
also referenced under: Book 70, Hadith 27 (In-Book) & Hadith 5399 (DarusSalam)