Avos, chapter 3, reads in part:
הוּא הָיָה אוֹמֵר חָבִיב אָדָם שֶׁנִּבְרָא בְצֶלֶם חִבָּה יְתֵרָה נוֹדַעַת לוֹ שֶׁנִּבְרָא בְצֶלֶם שֶׁנֶּאֱמַר כִּי בְּצֶלֶם א׳ עָשָׂה אֶת הָאָדָם
Sefaria's translation (which I'm not certain is correct, but let's go with it because I can't do better):
He would say: Beloved is man, since he is created in the image [of God]. A deeper love - it is revealed to him that he is created in the image, as it says: "for in God's image He made man."
He cites Noach 9:6, "שֹׁפֵךְ דַּם הָאָדָם בָּאָדָם דָּמוֹ יִשָּׁפֵךְ כִּי בְּצֶלֶם אֱלֹהִים עָשָׂה אֶת הָאָדָם", as evidence that man was נברא בצלם. Why not cite instead the earlier verse where man was in fact נברא בצלם, viz B'reshis 1:26–27, "וַיֹּאמֶר א׳ נַעֲשֶׂה אָדָם בְּצַלְמֵנוּ כִּדְמוּתֵנוּ… וַיִּבְרָא א׳ אֶת הָאָדָם בְּצַלְמוֹ בְּצֶלֶם א׳ בָּרָא אֹתוֹ"?
Credits: Thanks to Sefaria for the vowels for Avos, and to Rabbi Avi Kannai from whom I heard this question.