Related for Chullin 274:34
והתנן
These are the things which have no fixed measure: the corner [of the field], the firstfruits, and the appearance-offering!<span class="x" onmousemove="('comment',' Heb. The offerings to be brought on appearing before the Lord at the three Festivals (in accordance with Deut. XVI, 16: They shall not appear before the Lord empty) are not limited in their value; but see Hag. 20.');"><sup>18</sup></span>
Tosefta Peah
These are the things that have no set amount: the peah, the bikkurim, the r'iyah, charity, and learning Torah. Peah has a minimum amount but does not have a maximum amount. [If] one makes his entire field peah, it is not peah.
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