"But if the ox was prone to goring in time past" (Exodus 21:29-30). Which is a forewarned ox? Any concerning which witnesses testified for three days. And a harmless one? One that ceased goring for three days; these are the words of Rabbi Yehuda. Rabbi Meir says: a forewarned ox is one concerning which they testified three times; and a harmless one is one that children may handle and it does not gore. What is Rabbi Yehuda's reason? Abaye said: "yesterday" is one, "in time past" is two, "the day before" is three, and "its owner did not guard it" refers to a fourth goring. Rava said: "yesterday" and "in time past" are one and the same, and this is what it means: if it was so the day before and the owner did not guard it now, he is liable. And Rabbi Meir, what is his reason? As it was taught, Rabbi Meir said: an inference a fortiori. If when its gorings were spread apart the owner is liable, when its gorings were close together how much more so. Rava said to him: the case of the zav [a man with a flux] disproves it, for if his sightings were spread apart he is impure, and if his sightings were close together he is pure. He said to him: Scripture says, "And this shall be his impurity in his flux" (Leviticus 15:3) it is a decree of Scripture and we do not learn from it. Rav Nachman said in the name of Rav Adda bar Ahava: the law follows Rabbi Yehuda, since Rabbi Yose agrees with him, and Rabbi Yose's reasoning is always sound. As it was taught: which is a forewarned ox? Any concerning which witnesses testified for three days. A harmless one? One that children may handle and it does not gore these are the words of Rabbi Yose. Rabbi Shimon says: a forewarned ox is one concerning which they testified three times, and they said "three days" only with regard to its ceasing. "But if the ox was prone to goring": Scripture comes to distinguish between the harmless ox and the forewarned ox. Five matters lie between the harmless ox and the forewarned ox. The forewarned ox requires witnesses; the harmless ox does not require witnesses. The forewarned ox pays ransom; the harmless ox is exempt from ransom. The forewarned ox pays thirty shekels; the harmless ox does not pay thirty shekels. The forewarned ox pays full damages; the harmless ox pays half damages. The forewarned ox pays from the owner's best property; the harmless ox pays from its own body. "In time past, and warning was given to its owner" this tells that he is not liable until they warned him for three days.
How an Ox Becomes Forewarned and Five Laws Dividing Tam From Muad
Yalkut Shimoni on Torah 339:11
(שמות כא כט-ל) וְאִם שׁוֹר נַגָּח הוּא מִתְּמֹל שִׁלְשֹׁם, אֵיזֶהוּ מוּעָד, כָּל שֶׁהֵעִידוּ בּוֹ שְׁלֹשָׁה יָמִים. וְתָם, שֶׁחָזַר בּוֹ שְׁלֹשָׁה יָמִים, דִּבְרֵי רַבִּי יְהוּדָה. רַבִּי מֵאִיר אוֹמֵר, וּמוּעָד שֶׁהֵעִידוּ בּוֹ שְׁלֹשָׁה (יָמִים) [פְעָמִים]. וְתָם, שֶׁיְּהוּ הַתִּינוֹקוֹת מְמַשְׁמְשִׁין בּוֹ וְאֵינוֹ נוֹגֵחַ. מַאי טַעְמָא דְרַבִּי יְהוּדָה, אֲמַר אַבַּיֵּי, תְּמֹל חָד, מִתְּמֹל תְּרֵי, שִׁלְשֹׁם תְּלָתָא, וְלֹא יִשְׁמְרֶנּוּ בְּעָלָיו אֲתָא לִנְגִיחָה רְבִיעִית. רָבָא אָמַר, תְּמֹל וּמִתְּמֹל חָד הוּא. וְהָכִי קָאָמַר, אִם מִתְּמֹל שִׁלְשֹׁם הוּא וְלֹא יִשְׁמְרֶנּוּ הָאִידְנָא, חַיָּב. וְרַבִּי מֵאִיר, מַאי טַעְמָא, דְּתַנְיָא אָמַר רַבִּי מֵאִיר, קַל וָחֹמֶר, אִם רִחֵק נְגִיחוֹתָיו חַיָּב, קֵרֵב נְגִיחוֹתָיו לֹא כָּל שֶׁכֵּן. אֲמַר לֵיהּ רָבָא, (רְאִיָּה) [זִיבָה] תוֹכִיחַ, רִחֲקָה רְאִיּוֹתֶיהָ טְמֵאָה קֵרְבָה רְאִיּוֹתֶיהָ טְהוֹרָה. אֲמַר לֵיהּ, הֲרֵי הוּא אוֹמֵר (ויקרא טו, ג) "וְזֹאת תִּהְיֶה טֻמְאָתוֹ בְּזוֹבוֹ", גְּזֵרַת הַכָּתוּב הִיא וְלֹא יָלְפִינָן מִינָּהּ. אָמַר רַב נַחְמָן אֲמַר רַב אַדָא בַּר אֲהָבָה, הֲלָכָה כְּרַבִּי יְהוּדָה שֶׁהֲרֵי רַבִּי יוֹסֵי מוֹדֶה לוֹ, וְרַבִּי יוֹסֵי נִמּוּקוֹ עִמּוֹ. דְּתַנְיָא, אֵיזֶהוּ מוּעָד, כָּל שֶׁהֵעִידוּ בּוֹ שְׁלֹשָׁה יָמִים. תָּם, שֶׁיְּהוּ הַתִּינוֹקוֹת מְמַשְׁמְשִׁין בּוֹ וְאֵינוֹ נוֹגֵחַ (כְּרַבִּי) [דִּבְרֵי רַבִּי] יוֹסֵי. רַבִּי שִׁמְעוֹן אוֹמֵר, מוּעָד שֶׁהֵעִידוּ בּוֹ שְׁלֹשָׁה פְעָמִים, וְלֹא אָמְרוּ שְׁלֹשָׁה יָמִים אֶלָּא לְעִנְיַן חֲזָרָה בִּלְבַד. וְאִם שׁוֹר נַגָּח הוּא, בָּא הַכָּתוּב לַחֲלֹק בֵּין שׁוֹר תָּם לְמוּעָד. חֲמִשָּׁה דְּבָרִים בֵּין שׁוֹר תָּם לְמוּעָד, מוּעָד צָרִיךְ עֵדִים, וְתָם אֵינוֹ צָרִיךְ עֵדִים. מוּעָד מְשַׁלֵּם אֶת הַכֹּפֶר, וְתָם פָּטוּר מִן הַכֹּפֶר. מוּעָד מְשַׁלֵּם שְׁלֹשִׁים שְׁקָלִים, וְתָם אֵינוֹ מְשַׁלֵּם שְׁלֹשִׁים שְׁקָלִים. מוּעָד מְשַׁלֵּם נֵזֶק שָׁלֵם, וְתָם מְשַׁלֵּם חֲצִי נֵזֶק. מוּעָד מְשַׁלֵּם מִן הָעֲלִיָּה, וְתָם מְשַׁלֵּם מִגּוּפוֹ. [מִתְּמֹל שִׁלְשֹׁם] וְהוּעַד בִּבְעָלָיו, מַגִּיד שֶׁאֵינוֹ חַיָּב עַד שֶׁהִתְרוּ בּוֹ שְׁלֹשָׁה יָמִים.