Sunan Abi Dawud 3300
سنن أبي داود#3300SahihNarrated Ibn 'Abbas:While the Prophet (ﷺ) was preaching a man was standing in the sun. He asked about him. They said: He is Abu Isra'il who has taken a vow to stand and not to sit, or go into shade, or speak, but to fast. Thereupon he said: Command him to speak, to go into the shade, sit and complete his fast
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
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Bukhari (6704)
In-book reference: 22:59