The Shulchan Aruch · Yoreh De'ah
יורה דעה רכ״הYoreh De'ah 225
Siman 225 of 402 in Yoreh De'ah — 1 se'if
Se’if 1א׳
הָאוֹמֵר לַחֲבֵרוֹ פֵּירוֹתָיו שֶׁל פְּלוֹנִי אֲסוּרִין עָלֶיךָ, אֵינוֹ כְּלוּם אֶלָּא אִם כֵּן עָנָה הַנֶּאֱסָר: אָמֵן.
One who says to his fellow: the fruits of such a one are forbidden upon you — it is nothing, unless the one forbidden answered: Amen.
Shulchan Aruch, Yoreh De'ah — Torat Emet 357 edition, via Sefaria — public domain
English rendered from the Hebrew for this app — The Gematria's own rendering program. A rendering of the words, not a ruling; practical halacha is learned with a rav