עֵ֚ד הַגַּ֣ל הַזֶּ֔ה וְעֵדָ֖ה הַמַּצֵּבָ֑ה אִם־אָ֗נִי לֹֽא־אֶֽעֱבֹ֤ר אֵלֶ֙יךָ֙ אֶת־הַגַּ֣ל הַזֶּ֔ה וְאִם־אַ֠תָּה לֹא־תַעֲבֹ֨ר אֵלַ֜י אֶת־הַגַּ֥ל הַזֶּ֛ה וְאֶת־הַמַּצֵּבָ֥ה הַזֹּ֖את לְרָעָֽה׃
Zeuge sei dieser Steinhaufen, und Zeuge sei dieses Denkmal, dass ich niemals zu dir über diesen Steinhaufen hinübergehe und du niemals zu mir über diesen Steinhaufen und über dieses Denkmal in böser Absicht hinübergehst.
Rashi on Genesis
אם אני THAT I WILL NOT — Here the word אם is used in the sense of אשר “that”, as (Genesis 24:33) “until that (אם) I have spoken my words”.
Radak on Genesis
עד...אם אני, the expression אם אני and אם אתה in this verse must be understood as if the Torah had written שאני and שאתה, “that I,“ “that you.” We find the word אם used in that sense in Genesis 24,19 עד אם כלו לשתות, “until they have finished drinking,” as we pointed out there.
Tur HaArokh
עד הגל הזה, “this pile of stones is a witness, etc.” This is why Bileam (re-incarnate of Lavan) had his foot squeezed against the wall by the she-ass when he was on the way to curse the descendants of Yaakov, the “wall” described in Numbers The “wall” is a euphemism for this pile of stones, Bileam, being the re-incarnate of Lavan. [this may account for the fact that when Bileam arrived at Balak he was limping. Ed.]