Reference for Pesachim 78:13

<big><strong>גמ׳</strong></big> תנו רבנן אלו דברים שאין באין לידי חימוץ האפוי והמבושל וחלוט שחלטו ברותחין מבושל אדמבשל ליה מחמע אמר רב פפא האפוי שבישלו קאמר

On R'Akiba's view,<span class="x" onmousemove="('comment',' v. supra 36a.');">¹⁶</span> there is no question: seeing that he discharges his obligation [there with] in the case unleavened bread, [the tithing of] which is [enjoined] by Scripture. need you ask about maror, which is [only] Rabbinical.<span class="x" onmousemove="('comment',' By scriptural law vegetables need not be tithed at all; hence Biblically speaking this maror is not second tithe.');">¹⁷</span>

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