אַל־תִּתֵּן֙ אֶת־אֲמָ֣תְךָ֔ לִפְנֵ֖י בַּת־בְּלִיָּ֑עַל כִּֽי־מֵרֹ֥ב שִׂיחִ֛י וְכַעְסִ֖י דִּבַּ֥רְתִּי עַד־הֵֽנָּה׃
Count not thy handmaid for a wicked woman: for out of the abundance of my complaint and my vexation have I spoken hitherto.’
Siftei Chakhamim
Do not say this (לא תאמר כן)... Rashi added in the wordsתאמר כן (say this) because Yoseif had declared them as spies, so the proper word [to deny this] would be אַל. So we see with Channah (Shmuel I, 1:16). Eli thought she was a drunk, and she replied [in denial]: אַל תתן אמתך לפני בת בליעל. Whereas לא [when standing alone] is the proper reply to a question or a request.