Sahih al-Bukhari 6704
صحيح البخاري#6704SahihNarrated Ibn `Abbas:While the Prophet (ﷺ) was delivering a sermon, he saw a man standing, so he asked about that man. They (the people) said, "It is Abu Israil who has vowed that he will stand and never sit down, and he will never come in the shade, nor speak to anybody, and will fast.'' The Prophet (ﷺ) said, "Order him to speak and let him come in the shade, and make him sit down, but let him complete his fast
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: 83:81