Sahih al-Bukhari 1908
صحيح البخاري#1908SahihNarrated Ibn `Umar:The Prophet (ﷺ) said, "The month is like this and this," (at the same time he showed the fingers of both his hands thrice) and left out one thumb on the third time
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 30:18