Yevamos12: 2
חָלְצָה בְסַנְדָּל שֶׁאֵינוֹ שֶׁלּוֹ, אוֹ בְסַנְדָּל שֶׁל עֵץ, אוֹ בְשֶׁל שְׂמֹאל בַּיָּמִין — חֲלִיצָתָהּ כְּשֵׁרָה. חָלְצָה בְגָדוֹל שֶׁהוּא יָכוֹל לְהַלֵּךְ בּוֹ, אוֹ בְקָטָן שֶׁהוּא חוֹפֶה אֶת רֹב רַגְלוֹ — חֲלִיצָתָהּ כְּשֵׁרָה. חָלְצָה בַלַּיְלָה — חֲלִיצָתָהּ כְּשֵׁרָה; וְרַבִּי אֱלִיעֶזֶר פּוֹסֵל. בִּשְׂמֹאל — חֲלִיצָתָהּ פְּסוּלָה; וְרַבִּי אֱלִיעֶזֶר מַכְשִׁיר.
[If] she performed chalitzah with a sandal that was not his, or with a wooden sandal, or with a left shoe [placed] on his right [foot], her chalitzah is valid. [If] she performed chalitzah with a [sandal] which was [too] large [for him, but] in which he could [still] walk, or with a [sandal] which was [too] small [for him, but] which covered most of his foot, her chalitzah is valid. [If] she performed chalitzah at night, her chalitzah is valid; but R' Eliezer invalidates [it]. On the left [foot], her chalitzah is not valid; but R' Eliezer validates [it].
Yevamos12: 3
חָלְצָה וְרָקְקָה, אֲבָל לֹא קָרְאָה — חֲלִיצָתָהּ כְּשֵׁרָה. קָרְאָה וְרָקְקָה, אֲבָל לֹא חָלְצָה — חֲלִיצָתָהּ פְּסוּלָה. חָלְצָה וְקָרְאָה, אֲבָל לֹא רָקְקָה — רַבִּי אֱלִיעֶזֶר אוֹמֵר: חֲלִיצָתָהּ פְּסוּלָה; רַבִּי עֲקִיבָא אוֹמֵר: חֲלִיצָתָהּ כְּשֵׁרָה. אָמַר רַבִּי אֱלִיעֶזֶר: ,,כָּכָה יֵעָשֶׂה” — כָּל דָּבָר שֶׁהוּא מַעֲשֶׂה מְעַכֵּב. אָמַר לוֹ רַבִּי עֲקִיבָא: מִשָּׁם רְאָיָה? ,,כָּכָה יֵעָשֶׂה לָאִישׁ” — כָּל דָּבָר שֶׁהוּא מַעֲשֶׂה בָאִישׁ.
[If] she removed [the shoe] and spat, but did not recite, her chalitzah is [nevertheless] valid. [If] she recited and spat, but did not remove [the shoe], her chalitzah is not valid. [If] she removed [the shoe] and recited, but did not spit —- R' Eliezer says: her chalitzah is not valid; [but] R' Akiva says: her chalitzah is valid. Said R' Eliezer: ... So should be done ... (Deut. 25:9) —- whatever is an action is indispensable. R' Akiva replied: Is that a proof? “So should be done to the man ...” —- whatever is an action involving the man [is indispensable].