TT #126 · Parshas Shemini · Aliyah 6 · Passuk 11
Chabad.org — Vayikra Chapter 11 with Rashi
English: Everything in the water that has no fins and scales shall be an abomination for you.
Chullin 67b.
E-Daf.com — Chullin 67b (Tsurras Hadaf)
מִבְּשָׂרָם לֹא תֹאכֵלוּ. תָּנוּ רַבָּנַן, מִמַּשְׁמָע שֶׁנֶּאֱמַר אֱכֹל אֶת שֶׁיֵּשׁ לוֹ שׁוֹמֵעַ אֲנִי אַל תֹּאכַל אֶת שֶׁאֵין לוֹ, וְלָמָּה שְׁנָאָן לַעֲבֹר עָלָיו בַּעֲשֵׂה וְלֹא תַעֲשֶׂה.
Double prohibition — Repeating the prohibition establishes liability through both a positive command and a prohibition.
The repeated formulation is used to establish both positive and negative dimensions of the dietary prohibition.