What is the origin of the Jewish practice of "sitting shiva?" I just spent some time studying the "Book of Job." I thought I remembered reading somewhere that when Job’s friends sit with him for seven days without talking, it was the origin of the practice of sitting shiva. I couldn’t find the reference when I went to write about it. Other’s I consulted were doubtful. They suspected that the scene in Job was them doing something that was already done at the time. Thanks!

The Torah instructs us to mourn only one day after the burial. Chazal lengthened the time to a week. We find that King David sat on the ground after the death of his son, and at evening his servants raised him back to his feet. Rabbi Ro'i Margalit