Narrated Ibn 'Abbas:

While the Prophet 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 ﷺ يَخْطُبُ إِذَا هُوَ بِرَجُلٍ قَائِمٍ فَسَأَلَ عَنْهُ فَقَالُوا أَبُو إِسْرَائِيلَ نَذَرَ أَنْ يَقُومَ وَلاَ يَقْعُدَ وَلاَ يَسْتَظِلَّ وَلاَ يَتَكَلَّمَ وَيَصُومَ. فَقَالَ النَّبِيُّ ﷺ " مُرْهُ فَلْيَتَكَلَّمْ وَلْيَسْتَظِلَّ وَلْيَقْعُدْ وَلْيُتِمَّ صَوْمَهُ ". قَالَ عَبْدُ الْوَهَّابِ حَدَّثَنَا أَيُّوبُ، عَنْ عِكْرِمَةَ، عَنِ النَّبِيِّ ﷺ.