Sifrei Bamidbar 16

(Bamidbar 5:23) "Then the Cohein shall write the curses (these"): I might think, all the curses in the Torah (written in the curses of the covenant); it is, therefore, written "these." "the Cohein": What is the intent of this (i.e., is it not understood from the context?) For it would follow: It is written here "and he shall write," and it is written elsewhere (Devarim 24:1) "and he shall write" (a scroll of divorce). Just as there, any man may write it, so, here, (I would say that) any man may write it. It is, therefore, written "the Cohein." "and erase it": (He must write it) on something that can be erased. Now does this not follow a fortiori, viz.: If in order to make peace between a man and his wife, the L-rd said: A scroll written in holiness — let it be erased by the waters, then the scrolls of heretics, which inject (into the world) contempt and hatred and envy and contention — how much more so should they be erased from the world! R. Yishmael says: How does one deal with the scrolls of the heretics? He cuts out the "mentionings" (of G-d's name) and burns the rest. R. Akiva says: He burns them entire, for they were not written in holiness. "into a scroll": From here they ruled: It is not to be written on a tablet, or on paper, nor on hide, but on a scroll (of finished parchment). And he is not to write it with gummed ink or with vitriol, but with ink, it being written "and erase it into the bitter waters" — writing that can be erased. "and erase it into the bitter waters": the connotation is that the writing makes the waters bitter.