Bar Kappara said: Whoever calls Abraham "Abram" transgresses a positive commandment. Rabbi Levi said: A positive commandment and a negative commandment. "Your name shall no longer be called Abram" (Genesis 17:5), here is the negative commandment; "but your name shall be Abraham" (Genesis 17:5), here is the positive commandment. But did not the Men of the Great Assembly call him "Abram"? "You are the LORD God who chose Abram" (Nehemiah 9:7). It is different, for while he was still Abram You chose him. And likewise, one who calls Sarah "Sarai" transgresses a positive commandment, for it is she concerning whom he was commanded. And likewise, one who calls Israel "Jacob" transgresses a positive commandment. It was taught: Not that the name Jacob should be uprooted, but "for Israel shall be your name" (Genesis 35:10) means Israel is primary and Jacob secondary. Rav Zechariah in the name of Rav Acha said: In any case Jacob is his name, but "for Israel shall be your name" means Jacob is primary and Israel is added upon it.
Whoever Calls Abraham by His Old Name Transgresses
Yalkut Shimoni on Torah 81:16
בַּר קַפָּרָא אָמַר, כָּל הַקּוֹרֵא לְאַבְרָהָם אַבְרָם עוֹבֵר בַּעֲשֵׂה. אָמַר רַבִּי לֵוִי, בַּעֲשֵׂה וְלֹא תַּעֲשֵׂה, "וְלֹא יִקָּרֵא עוֹד אֶת שִׁמְךָ אַבְרָם", הֲרֵי בְּלֹא תַּעֲשֶׂה, "וְהָיָה שִׁמְךָ אַבְרָהָם", הֲרֵי בַּעֲשֵׂה. וַהֲרֵי אַנְשֵׁי כְּנֶסֶת הַגְּדוֹלָה קְרָאוּהוּ אַבְרָם (נחמיה ט, ז) "אַתָּה הוּא ה' הָאֱלֹהִים אֲשֶׁר בָּחַרְתָּ בְּאַבְרָם". שַׁנְיָא הִיא שֶׁעַד שֶׁהוּא אַבְרָם בָּחַרְתָּ בּוֹ וְדִכְוָתֵהּ הַקּוֹרֵא שָׂרַי עוֹבֵר בַּעֲשֵׂה, (וְלֹא) הוּא שֶׁנִּצְטַוָּה עָלֶיהָ וְדִכְוָתֵהּ הַקּוֹרֵא לְיִשְׂרָאֵל יַעֲקֹב עוֹבֵר בַּעֲשֵׂה, תָּנִי, לֹא שֶׁיֵּעָקֵר שֵׁם יַעֲקֹב, אֶלָּא (בראשית לה, י) "כִּי אִם יִשְׂרָאֵל יִהְיֶה שְׁמֶךָ", יִשְׂרָאֵל עִקָּר וְיַעֲקֹב טָפֵל רַב זְכַרְיָה בְּשֵׁם רַב אָחָא אָמַר, מִכָּל מָקוֹם יַעֲקֹב שְׁמוֹ אֶלָּא "כִּי אִם יִשְׂרָאֵל יִהְיֶה שְׁמֶךָ", יַעֲקֹב עִקָּר וְיִשְׂרָאֵל מוֹסִיף עָלָיו.