(44, 45) باب عَقْلِ الأَصَابِعِ
It was narrated from Ibn 'Abbas that the Propher said:
"this and this are the same,": meaning the little finger and the thumb.
Reference: Sunan an-Nasa'i 4847
In-book reference: Book 45, Hadith 142
English translation: Vol. 5, Book 45, Hadith 4851