All the commandments of a son that fall upon the father to perform for his son: men are obligated and women are exempt. We learned this from what the Rabbis taught: A man is obligated regarding his son to circumcise him, to redeem him, to teach him Torah, to marry him to a wife, and to teach him a craft; and some say even to teach him to swim in the river. Rabbi Yehudah says: Anyone who does not teach his son a craft, it is as though he teaches him robbery. From where do we learn the obligation to circumcise him? As it is written, "And Abraham circumcised Isaac his son when he was eight days old, as God had commanded him." "Him" [the son] and not "her" [a daughter]. And where the father does not circumcise him, the court is obligated to circumcise him, as it is written (Genesis 17:10), "Every male among you shall be circumcised." And where the court does not circumcise him, he is obligated to circumcise himself, as it is written, "And an uncircumcised male who is not circumcised" and so on. We have found the obligation for the immediate case; from where do we learn it for future generations? The school of Rabbi Yishmael taught: Wherever "command" is stated, it means nothing other than an urging, both immediately and for future generations. Urging, as it is written (Deuteronomy 3:28), "And command Joshua and strengthen him and embolden him." Immediately and for future generations, as it is written, "From the day that the LORD commanded and onward, throughout your generations."
A Father's Duties to His Son and the Source for Circumcision
Yalkut Shimoni on Torah 92:3
כָּל מִצְווֹת הַבֵּן הַמּוּטָלוֹת עַל הָאָב לַעֲשׂוֹת לִבְנוֹ, אֲנָשִׁים חַיָּבִים וְנָשִׁים פְּטוּרוֹת. תָּנִינָא לְהָא דְּתָנוּ רַבָּנָן חַיָּב אָדָם לִבְנוֹ לְמוּלוֹ, וְלִפְדּוֹתוֹ, וּלְלַמְּדוֹ תּוֹרָה, וּלְהַשִּׂיאוֹ אִשָּׁה, וּלְלַמְּדוֹ אוֹמָנוּת, וְיֵשׁ אוֹמְרִים אַף לְהַשִּׁיטוֹ בַּנָּהָר רַבִּי יְהוּדָה אוֹמֵר, כָּל שֶׁאֵינוֹ מְלַמֵּד אֶת בְּנוֹ אוֹמָנוּת כְּאִלּוּ מְלַמְּדוֹ לִיסְטִיּוּת לְמוּלוֹ מְנָא לָן דִּכְתִיב, וַיָּמָל אַבְרָהָם אֶת יִצְחָק בְּנוֹ בֶּן שְׁמֹנַת יָמִים כַּאֲשֶׁר צִוָּה אֹתוֹ, אוֹתוֹ וְלֹא אוֹתָה וְהֵיכָא דְּלֹא מַהַלֵיה אַבוּהָ מִיחַיְּבֵי בֵּי דִינָא לְמִימְהַלֵיה, דִכְתִיב (בראשית יז, י) "הִמּוֹל לָכֶם כָּל זָכָר", וְהֵיכָא דְלֹא מַהַלֵיה בֵּית דִין מִיחַיֵּב אִיהוּ לְמִימְהַל נַפְשֵׁיה דִּכְתִיב, "וְעָרֵל זָכָר אֲשֶׁר לֹא יִמּוֹל" וְגוֹ'. אַשְׁכָּחָן מִיָּד, לְדוֹרוֹת מְנָא לָן, תָּנָא דְּבֵי רַבִּי יִשְׁמָעֵאל, כָּל מָקוֹם שֶׁנֶּאֱמַר צַוָּאָה, אֵינוֹ אֶלָּא זֵרוּז מִיָּד וּלְדוֹרוֹת. זֵרוּז דִּכְתִיב, (דברים ג, כח) "וְצַו אֶת יְהוֹשֻׁעַ וְחַזְּקֵהוּ וְאַמְּצֵהוּ". מִיָּד וּלְדוֹרוֹת, דִּכְתִיב, "מִן הַיּוֹם אֲשֶׁר צִוָּה ה' וְהָלְאָה לְדוֹרוֹתֵיכֶם".