Flowing sand. Al-Kalbi said: “It is sand such that, when you take some of it, what remains follows after it. One says, ‘I caused the sand to flow,’ when one stirs its lower part until it pours down from above.”

“Indeed, We have sent to you a Messenger as a witness over you, just as We sent a messenger to Pharaoh. But Pharaoh disobeyed the messenger, so We seized him with a crushing seizure. How, then, will you protect yourselves, if you disbelieve, from a Day that will turn children grey-haired, by which the heaven will be split apart? His promise is sure to be fulfilled. Indeed, this is a reminder; so whoever wills may take a path to his Lord.” (15–19)