While the Prophet ﷺ was delivering a sermon, he noticed a man standing. He asked about him, and the people said, "That is Abu Israil. He has vowed to remain standing without sitting, not to seek shade, not to speak, and to fast."The Prophet ﷺ said, "Tell him to speak, to seek shade, and to sit, but to complete his fast."
بينا النبي ﷺ يخطب إذا هو برجل قائم، فسأل عنه فقالوا: أبو إسرائيل نذر أن يقوم ولا يقعد، ولا يستظل، ولا يتكلم، ويصوم. فقال النبي ﷺ: مره فليتكلم وليستظل وليقعد، وليتم صومه.
Bukhari narrated it in "Oaths and Vows" (6704), from Musa bin Ismail, who said, Wahib narrated to us, who said, Ayub narrated to us, from Ikrima, from Ibn Abbas, who mentioned it. This Abu Israil was a man from the Ansar, and it is said his name was Yasir, as Ibn Abdul-Barr mentioned in "al-Istiab."