'I once went to visit Abu 'Abdillah [al-Sadiq] (AS) along with one of our companions. I said to him, ?O son of the Prophet! Could I but sacrifice myself for you. I grieve and become sorrowful without knowing the cause of that.' So Abu 'Abdillah (AS) replied, 'Truly that sorrow and joy reaches you from us, for when sorrow or joy comes to us it comes to you too, for indeed we and you are all from the Light of Allah, Mighty and Exalted.?