Abdullah bin Abbas (may Allah be pleased with them both) narrates: Once the Prophet Muhammad (peace be upon him) was delivering a sermon when he saw a man standing in the sun. He inquired about him. The people said: This is Abu Isra'il. He has vowed to stand in the sun, not to sit, not to come into the shade, not to speak to anyone, and not to break his (voluntary) fast. The Prophet Muhammad (peace be upon him) said: Tell him to sit down, come into the shade, speak to others, and to continue or break his (voluntary) fast as he wishes.