Reference for Zevachim 150:6

א"ר יוסי בר זבידא ת"ש נתערבו בבכור ובמעשר ירעו עד שיסתאבו ויאכלו כבכור וכמעשר לאו למימרא דאינו נשקל בליטרא

GEMARA. A Tanna recited before Rab: You must not purchase terumah with the money of seventh-year produce, because you diminish the time allowed for its consumption. The Rabbis stated in Rabbah's presence: This does not agree with R. Simeon, for if it agreed with R. Simeon, surely he maintained: One may bring sacrifices to the place of unfitness. Said he to them: You may say that it agrees even with R. Simeon: That is only when it was done, but not at the very outset. 'But not at the outset'? Abaye raised an objection to him:

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