Reference for Gittin 5:7
חֵרֵשׁ רוֹמֵז וְנִרְמָז. וּבֶן בְּתֵירָא אוֹמֵר, קוֹפֵץ וְנִקְפָּץ, בְּמִטַּלְטְלִין. הַפָּעוֹטוֹת, מִקָּחָן מִקָּח וּמִמְכָּרָן מִמְכָּר, בְּמִטַּלְטְלִין:
A deaf-mute gestures and is gestured to. [Whatever he gestures or others gesture to him and he acquiesces — all of it stands.] And Ben Betheirah says: kofetz venikfatz ["remizah" (gesturing) is with the hand or the head. "k'fitzah" is turning up the lips, as in (Job 5:16): "And iniquity has turned up (kaftzah) her mouth." "K'fitzah is not as distinct as remizah.] with metaltelin (chattel) [i.e., if he sold chattel. The halachah is not in accordance with Ben Betheirah.] Peutoth [young children of seven or eight, if they are bright and conversant with buying and selling; or children of nine or ten, even if they are not that bright] — their buying is buying and their selling is selling with metaltelin [and their gift is a gift, whether they be healthy or shechiv mera (at the point of death); whether it be a large or a small gift.]