Sunan an-Nasa'i, Hadith 4848 ⓘ
It was narrated from Ibn 'Abbas: "This and this are the same: The little finger and the thumb (sahih)
أَخْبَرَنَا نَصْرُ بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، فَهَذِهِ وَهَذِهِ سَوَاءٌ الإِبْهَامُ وَالْخِنْصَرُ .
also referenced under: Book 45, Hadith 143 (In-Book) & Volume 5, Book 45, Hadith 4852 (DarusSalam)