Mishkat al-Masabih
He reported God’s messenger as saying, "When food is set down take off your sandals, for it gives more rest to your feet."
وَعَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا وُضِعَ الطَّعَامُ فَاخْلَعُوا نِعَالَكُمْ فإِنَّه أرْوَحُ لأقدامكم»
Reference