What one is not given permission for

A'yan al-Khwarizmi said, "We came to Anas ibn Malik while he was sitting his foyer with anyone else with him. My companion greeted him and said, 'May I come in?' Anas said, 'Come in. This is a place where no one asks for permission.' He had food brought to us and we ate. Then a cup of sweet nabidh was brought and we drank and were full."

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، قَالَ: حَدَّثَنَا أَعْيَنُ الْخُوَارِزْمِيُّ قَالَ: أَتَيْنَا أَنَسَ بْنَ مَالِكٍ، وَهُوَ قَاعِدٌ فِي دِهْلِيزِهِ وَلَيْسَ مَعَهُ أَحَدٌ، فَسَلَّمَ عَلَيْهِ صَاحِبِي وَقَالَ: أَدْخُلُ؟ فَقَالَ أَنَسٌ: ادْخُلْ، هَذَا مَكَانٌ لاَ يَسْتَأْذِنُ فِيهِ أَحَدٌ، فَقَرَّبَ إِلَيْنَا طَعَامًا، فَأَكَلْنَا، فَجَاءَ بِعُسِّ نَبِيذٍ حُلْوٍ فَشَرِبَ، وَسَقَانَا.