Mukhtasar Bukhari

Narrated Ibn Abbas (may Allah be pleased with them) that once the Prophet Muhammad (peace be upon him) was delivering a sermon when he saw a man standing. The Prophet (peace be upon him) inquired: "Who is this man?" The people replied, "He is Abu Isra'il. He has vowed to stand (all day), not to sit, not to seek shade, not to speak to anyone, and to complete his fast in this state." The Prophet (peace be upon him) said: "Tell him to sit down, come into the shade, speak, and complete his fast (in this manner)."