תּלמוד אויף שמות 10:12

And they both derive their views from [the same statement] of Rebbi Yehudah. For It was taught in a barasia, (Exodus 12, 10) "And do not leave anything over until morning. And anything leftover until morning [must be burned in fire] etc." the Torah comes to give a positive commandment following a negative commandment to teach that he is not liable to malkus. These are the words of Rebbi Yehudah. Rebbi Yochanon expounds thus, the reason [Rebbi Yehudah says that he isn't flogged] is because the Torah comes [with a remedial positive commandment], but if the Torah would not have came then he would be flogged. We therefore see that a questionable warning constitutes as a valid warning.