四分律刪繁補闕行事鈔 1.149

1.149

瘂聾等三，由根不具，不成證故。大德僧聽，不忍者說；並闕二能，故不足也。準《伽論》云：若聞大語聲者，得成法事。

The three, including the mute and deaf: because their sense faculties are incomplete, they do not serve as witnesses. When 'the Venerable Saṃgha listens,' those who do not approve speak; since both abilities are lacking, they do not make up the quorum. According to the [Vinayamātṛkā] Śāstra, it states: 'If one hears the sound of a loud voice, the legal act is accomplished.'