Sunan an-Nasa'i, Volume 5, Book 45, Hadith 4851 (DarusSalam) ⓘ
It was narrated from Ibn 'Abbas that the Propher said: "this and this are the same,": meaning the little finger and the thumb.
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ حَدَّثَنِي قَتَادَةُ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، رضى الله عنهما عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " هَذِهِ وَهَذِهِ سَوَاءٌ " . يَعْنِي الْخِنْصَرَ وَالإِبْهَامَ .
also referenced under: Hadith 4847 (Reference) & Book 45, Hadith 142 (In-Book)