Sifrei Devarim 90

¹(Devarim 13:11) "And you shall stone him with stones and he shall die": I might think, with many stones; it is, therefore, written (Vayikra 24:23) "and they stoned him with a stone." If "with a stone," I would think with one stone! Say, then, if he did not die with the first, he is to be put to death with a second. ²"for he sought to turn you from the L-rd your G-d": "to turn you away" is written here, and, elsewhere, (in connection with a false prophet) (Devarim, Ibid . 6) "to turn you away." Just as here (his penalty is) stoning, so, there, stoning. ³"from the L-rd your G-d, who took you out of the land of Egypt": Even if your only indebtedness to Him were His taking you out of the land of Egypt, it would warrant (such a penalty).