Ibn 'Abbas (May Allah be pleased with them) reported:
While the Prophet ﷺ was delivering Khutbah (religious talk), he noticed a man who was standing, so he asked about him and was told that he was Abu Israel who had taken a vow to remain standing and not sit, or go into the shade, or speak while observing fasting. Thereupon Messenger of Allah ﷺ said, "Tell him to speak, to go into the shade, to sit and to complete his fast".

[Al-Bukhari].

- وعن ابن عباس رضي الله عنهما قال: بينما النبي ﷺ يخطب إذا هو برجل قائم، فسأل عنه فقالوا: أبو إسرائيل نذر أن يقوم في الشمس ولا يقعد، ولا يستظل ولا يتكلم، ويصوم، فقال النبي ﷺ: "مروه فليتكلم وليستظل وليقعد وليتم صومه" ((رواه البخاري)).