“The Messenger of Allah ﷺ forbade me to wear a ring on this and on this,” meaning the little finger and the thumb.  

نَهَانِي رَسُولُ اللَّهِ ﷺ أَنْ أَتَخَتَّمَ فِي هَذِهِ وَفِي هَذِهِ يَعْنِي الْخِنْصَرَ وَالإِبْهَامَ