"Zaid bin Harithah arrived in Al-Madinah while the Messenger of Allah ﷺ was in his house. So he went and knocked at the door, so the Messenger of Allah ﷺ stood naked (1), dragging his garment - and by Allah! I did not see him naked before nor afterwards - and he hugged him and kissed him." (1) They say that the meaning of naked here is that he was not wearing his Rida or upper wrap and it was that which was dragging, so the area between the navel and knees were covered. See Tuhfat Al-Ahwadhi.  

قَدِمَ زَيْدُ بْنُ حَارِثَةَ الْمَدِينَةَ وَرَسُولُ اللَّهِ ﷺ فِي بَيْتِي فَأَتَاهُ فَقَرَعَ الْبَابَ فَقَامَ إِلَيْهِ رَسُولُ اللَّهِ ﷺ عُرْيَانًا يَجُرُّ ثَوْبَهُ وَاللَّهِ مَا رَأَيْتُهُ عُرْيَانًا قَبْلَهُ وَلاَ بَعْدَهُ فَاعْتَنَقَهُ وَقَبَّلَهُ