Sunan an-Nasa'i, Book 48, Hadith 174 (In-Book) ⓘ
It was narrated from Anas that: When entering the Khala', the Messenger of Allah [SAW] would take off his ring.
أَخْبَرَنَا مُحَمَّدُ بْنُ إِسْمَاعِيلَ بْنِ إِبْرَاهِيمَ، عَنْ سَعِيدِ بْنِ عَامِرٍ، عَنْ هَمَّامٍ، عَنِ ابْنِ جُرَيْجٍ، عَنِ الزُّهْرِيِّ، عَنْ أَنَسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا دَخَلَ الْخَلاَءَ نَزَعَ خَاتَمَهُ .
also referenced under: Hadith 5213 (Reference) & Volume 6, Book 48, Hadith 5216 (DarusSalam)