Reference for Gittin 142:11

אימא סיפא עד שיאמר לסופר כתוב ולעדים חתומו אתאן לר' יוסי דאמר מילי לא מימסרן לשליח

Or, I might have said, the word 'never' indicates the lesson taught by R. Isaac. For R. Isaac said: According to the rule of the [written] Torah, an insane wife can be divorced, being on the same footing as a sound woman who is divorced without her own consent. Why then did the Rabbis lay down that she should not be divorced? In order that she should not be used for immoral purposes.<span class="x" onmousemove="('comment',' The insertion of the word 'never' in the second clause is not intended to exclude the deaf-mute's divorce by writing, but is meant to indicate that the rule regarding the husband has the sanction of the Torah, whereas the one regarding the wife mentioned in the first clause has the sanction only of the Rabbis. ');">¹⁰</span>

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