Sunan Abi Dawud 4558
سنن أبي داود#4558SahihNarrated Ibn 'Abbas:The Messenger of Allah (ﷺ) as saying: This and that are equal, that is, the thumb and the little finger
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Zubair Ali ZaiSahih Bukhari (6895)
In-book reference: 41:65