DO NOT INFLICT UNNECESSARY HARDSHIPS UPON YOURSELF H H 153 While the Prophet, praise and peace be upon him, was delivering his sermon, he noticed a man standing up and inquired about him. He was told that his name was Abu Israel and that he had made a vow to keep standing in the sun. He would neither sit down, move into the shade, nor would he speak to anyone and he was fasting. The Prophet, praise and peace be upon him, said: 'Tell him to speak, and to move into the shade and sit down. But let him complete his fast.' R 153 Bukhari with a chain up to ibn Abbas who related this.
152- وعنِ ابن عباس رضي الله عنهما ، قَالَ : بينما النَّبيُّ صلى الله عليه وآله وسلم يخطب إِذَا هُوَ برجلٍ قائم فسأل عَنْهُ ، فقالوا : أَبُو إسْرَائيلَ نَذَرَ أنْ يَقُومَ في الشَّمْسِ وَلاَ يَقْعُدَ ، وَلاَ يَسْتَظِل ، وَلاَ يَتَكَلَّمَ ، وَيَصُومَ ، فَقَالَ النَّبيّ صلى الله عليه وآله وسلم : "مُرُوهُ ، فَلْيَتَكَلَّمْ ، وَلْيَسْتَظِلَّ ، وَلْيَقْعُدْ ، وَلْيُتِمَّ صَوْمَهُ" رواه البخاري .