Reference for Gittin 141:9

והא קתני ירושות אמר רבי אבהו ירושת בנו הבכור

This excludes a mute who cannot utter'. Now why should this be, seeing that [according to R. Kahana] he can signify by writing? — Abaye replied to him: You are speaking of testimony, and testimony comes under a different rule, because the All-Merciful has said that it must be from their mouths,<span class="x" onmousemove="('comment',' Deut. XIX, 15, 'At the mouth of two witnesses&nbsp;… shall a matter be established'. ');">⁹</span>

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