Mishkat al-Masabih 22 Clothing كتاب اللباس 80

وَعَنْهُ قَالَ: كَانَ خَاتَمُ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي هَذِهِ وَأَشَارَ إِلَى الْخِنْصِرِ منْ يَده الْيُسْرَى. رَوَاهُ مُسلم

He said, pointing to the little finger of his left hand, “The Prophet’s signet-ring was on this.” Muslim transmitted it.