Reference for Gittin 6:1
הָאוֹמֵר הִתְקַבֵּל גֵּט זֶה לְאִשְׁתִּי אוֹ הוֹלֵךְ גֵּט זֶה לְאִשְׁתִּי, אִם רָצָה לַחֲזֹר, יַחֲזֹר. הָאִשָּׁה שֶׁאָמְרָה, הִתְקַבֵּל לִי גִטִּי, אִם רָצָה לַחֲזֹר, לֹא יַחֲזֹר. לְפִיכָךְ, אִם אָמַר לוֹ הַבַּעַל, אִי אֶפְשִׁי שֶׁתְּקַבֵּל לָהּ אֶלָּא הוֹלֵךְ וְתֵן לָהּ, אִם רָצָה לַחֲזֹר, יַחֲזֹר. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר, אַף הָאוֹמֶרֶת טֹל לִי גִטִּי, אִם רָצָה לַחֲזֹר, לֹא יַחֲזֹר:
If one says: "Receive this get for my wife," or: "Deliver this get to my wife," if he wishes to rescind it, he may do so, [for a get is a liability for a woman, and one may not impose a liability upon another without his knowledge.] If a woman said (to a messenger): "Receive my get for me," if he wishes to rescind it, he may not do so, [for since she appointed him a messenger, he is like her "hand," and she is divorced immediately when he receives the get.] Therefore, if the husband said to him: "I do not want you to receive it for her, but go and give it to her," if he wishes to rescind it, he may do so. R. Shimon b. Gamliel says: Also, if she said: "Tol my get for me," if he wishes to rescind it, he may not do so." ["Tol" denotes "taking." The halachah is in accordance with R. Shimon b. Gamliel.]