Exodus 7:24

It is not much material to us, whether they lost their labour, and found only blood there, as Josephus affirms; or whether they succeeded and found water there, which seems more probable, because these come not within the compass of Moses's commission, Exodus 7:17,19,20, or whether they found the water something purified and less bloody, though mixed with blood. But it is observable, that though the devil could do something which might increase the plague, or imitate it, yet he could do nothing to remove it.