كتاب الأيمان والنذور
Oaths and Vows
Chapter: To vow for something not possessed, and for something sinful
باب النَّذْرِ فِيمَا لاَ يَمْلِكُ وَفِي مَعْصِيَةٍ
Sahih al-Bukhari 6704

Narrated 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."

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا وُهَيْبٌ، حَدَّثَنَا أَيُّوبُ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ بَيْنَا النَّبِيُّ صلى الله عليه وسلم يَخْطُبُ إِذَا هُوَ بِرَجُلٍ قَائِمٍ فَسَأَلَ عَنْهُ فَقَالُوا أَبُو إِسْرَائِيلَ نَذَرَ أَنْ يَقُومَ وَلاَ يَقْعُدَ وَلاَ يَسْتَظِلَّ وَلاَ يَتَكَلَّمَ وَيَصُومَ‏.‏ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏ "‏ مُرْهُ فَلْيَتَكَلَّمْ وَلْيَسْتَظِلَّ وَلْيَقْعُدْ وَلْيُتِمَّ صَوْمَهُ ‏"‏‏.‏ قَالَ عَبْدُ الْوَهَّابِ حَدَّثَنَا أَيُّوبُ، عَنْ عِكْرِمَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم‏.‏
Reference : Sahih al-Bukhari 6704
In-book reference : Book 83, Hadith 81
USC-MSA web (English) reference : Vol. 8, Book 78, Hadith 695
  (deprecated numbering scheme)