Tractate Tahorot - Chapter 5 - Mishnah 4 טהרות פרק ה׳ משנה ד׳

If there was a sheretz and a frog in a public domain and a man touched one of them and then prepared clean foods which were subsequently consumed; and then he immersed, and then he touched the other and then prepared clean foods, the latter are deemed clean. If the first foods were still in existence both must be held in suspense. If he did not immerse in the meanwhile, the first are held in suspense and the second must be burnt .