Reference for Nedarim 6:6
הַנּוֹדֵר מִן הַבָּשָׂר, מֻתָּר בַּרֹטֶב וּבַקִּפָּה. וְרַבִּי יְהוּדָה אוֹסֵר. אָמַר רַבִּי יְהוּדָה, מַעֲשֶׂה וְאָסַר עָלַי רַבִּי טַרְפוֹן בֵּיצִים שֶׁנִּתְבַּשְּׁלוּ עִמּוֹ. אָמְרוּ לוֹ, וְכֵן הַדָּבָר, אֵימָתַי, בִּזְמַן שֶׁיֹּאמַר בָּשָׂר זֶה עָלָי, שֶׁהַנּוֹדֵר מִן הַדָּבָר וְנִתְעָרֵב בְּאַחֵר, אִם יֶשׁ בּוֹ בְנוֹתֵן טַעַם, אָסוּר:
If one bevows himself from meat, he is permitted (to eat) meat-broth and keifeh. [Broth solidified at the bottom of the pot is called "keifeh."] R. Yehudah forbids it [since it has the flavor of meat. The halachah is not in accordance with R. Yehudah.] R. Yehudah said: "Once R. Tarfon forbade to me eggs which had been cooked with it!" They said to him: "So it should be! When is it so (that it is forbidden)? When he says: 'This meat (is forbidden) to me.'" [For since he said: "This meat," he forbade it to himself and forbade its taste. But if he said: "konam meat to me," he forbade to himself only what is called "meat."] For if one bevows himself from something and it becomes intermixed with something else, if there is in it (the bevowed thing) enough to impart its flavor (to the thing it is intermixed with), it is forbidden.