رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 746
The Book About the Etiquette of Eating
Undesirability of Eating in a Reclining Posture
وَعَنْ أَنَسٍ رضى اللَّهُ عَنْهُ قَالَ: رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ جالساً مقعياً يأكل تمراً. ((رَوَاهُ مُسْلِم))
Anas (May Allah be pleased with him) reported: I saw Messenger of Allah (ﷺ) eating some dates while sitting on his buttocks, with his legs raised. [Muslim].
Riyad as-Salihin, 746