Sayyiduna Abu Hurairah (may Allah be pleased with him) says that we were sitting with the Messenger of Allah (peace and blessings be upon him) when a loud sound was heard. The Prophet (peace and blessings be upon him) said, "Do you know what that was?" We replied, "Allah and His Messenger (peace and blessings be upon him) know best." He (peace and blessings be upon him) said, "That was a stone which was thrown into Hell seventy years ago. It has been falling, and now it has reached its bottom." (God forbid, Hell is so deep that from its top to its bottom is a journey of seventy years, and that too at the speed with which a stone falls from top to bottom.)