The Book of Clothes and Adornment
وَحَدَّثَنِي أَبُو بَكْرِ بْنُ خَلاَّدٍ الْبَاهِلِيُّ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ مَهْدِيٍّ، حَدَّثَنَا حَمَّادُ، بْنُ سَلَمَةَ عَنْ ثَابِتٍ، عَنْ أَنَسٍ، قَالَ كَانَ خَاتِمُ النَّبِيِّ صلى الله عليه وسلم فِي هَذِهِ . وَأَشَارَ إِلَى الْخِنْصَرِ مِنْ يَدِهِ الْيُسْرَى .Anas reported that the ring of Allah's Apostle (ﷺ) was on this, and he pointed toward the little finger of his left hand
From Sahih Muslim, whose reports the scholars accept as authentic.