I am assuming it is ash but was uncertain. The bars are cut and there was no ash on the top prior to cutting it. Will ash form slowly over time after it is cut, as it is curing?
You can wipe ash off with water. Give them a quick rinse under the sink or wipe them off with a damp cloth.
I've never seen ash form on the cut sides... just on the tops. You might tongue test it to be 100% sure. At least thats what I would do because I've never seen ash form on the cut sides. But I'm fairly new to soap making myself and might have just never seen any ash form there yet.