וְהֽוֹצֵאתָ֣ אֶת־הָאִ֣ישׁ הַה֡וּא אוֹ֩ אֶת־הָאִשָּׁ֨ה הַהִ֜וא אֲשֶׁ֣ר עָ֠שׂ֠וּ אֶת־הַדָּבָ֨ר הָרָ֤ע הַזֶּה֙ אֶל־שְׁעָרֶ֔יךָ אֶת־הָאִ֕ישׁ א֖וֹ אֶת־הָאִשָּׁ֑ה וּסְקַלְתָּ֥ם בָּאֲבָנִ֖ים וָמֵֽתוּ׃
you shall take the man or the woman who did that wicked thing out to the public place, and you shall stone them, that man or woman, to death.—
Torah Temimah points to Sifrei Devarim.
באבנים. יכול באבנים מרובות ת״ל (פ׳ אמור) באבן, אי באבן, יכול באבן אחת, ת״ל באבנים, הא כיצד, לא מת בראשונה ימות בשניה.
English: “With stones.” One might think [it requires] many stones; therefore the verse says (in Parashas Emor) “with a stone.” If [it says] “with a stone,” one might think a single stone [suffices even if it does not kill]; therefore it says “with stones.” How so? If he did not die from the first, he dies from the second.
The two expressions (“stone” and “stones”) together teach that one stone is sufficient if it kills, but additional stones are used if the first does not complete the execution.
Derash on the verse (Sifrei) — not a formal named middah of the 13. The singular and plural forms are reconciled to define the practical procedure of stoning.
Stoning begins with one stone; if that does not kill the condemned, further stones are used until death occurs.