TT #116 · Parshas Shemini · Aliyah 6 · Passuk 9
English: These you may eat among all that live in water: anything in the water, whether in the seas or in the streams, that has fins and scales—these you may eat.
Chullin 66b.
E-Daf.com — Chullin 66b (Tsurras Hadaf)
סְנַפִּיר וְקַשְׂקֶשֶׂת. כָּל שֶׁיֵּשׁ לוֹ קַשְׂקֶשֶׂת יֵשׁ לוֹ סְנַפִּיר, וְיֵשׁ שֶׁיֵּשׁ לוֹ סְנַפִּיר וְאֵין לוֹ קַשְׂקֶשֶׂת, וְלִכְתֹּב רַחֲמָנָא קַשְׂקֶשֶׂת וְלֹא בָּעֵי סְנַפִּיר, אָמַר רַבִּי אַבָּהוּ, יַגְדִּיל תּוֹרָה וְיַאְדִּיר.
Textual economy — Although every fish with scales also has fins, the Torah writes both signs in order to magnify Torah and make its teaching abundant.
A fish found with scales does not require a separate search for fins; the Torah nevertheless states both signs.