Hadith 13:35
Ibn ‘Abbas reported the Prophet as saying, “This and that are equal,” meaning the little finger and the thumb. Bukhari transmitted it.
عَنِ ابْنِ عَبَّاسٍ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «هَذِهِ وَهَذِهِ سَوَاءٌ» يَعْنِي الخِنصرُ والإبهامَ. رَوَاهُ البُخَارِيّ
Original Reference: Mishkat al-Masabih 3486