Reference for Moed Katan 5:22
מדרבנן וקרא אסמכתא בעלמא
Whence [is derived the rule] not to manure, or remove stones, [or dust] or fumigate the trees? From the instructive text: Thy field thou shalt not. thy vineyard thou shalt not. [that is], no manner of work in thy field, no manner of work in thy vineyard. Am I then to say that one may not stir the soil under the olive trees, nor use the hoe under the vines, nor fill the [open] gaps [under the olives] with water, nor make drills for the vines? There is the instructive wording of the text: Thy field thou shalt not sow and thy vineyard thou shalt not prune. Now, sowing was already embraced in the general terms of the ordinance, why then was it singled out [for mention]? For the purpose of providing [ground for] an analogy, that just as sowing has the special quality of being a work common to field and vineyard, so is any other work that is common to field and orchard [forbidden]? - [That is only] rabbinically; and the text is [adduced] as a mere support.<span class="x" onmousemove="('comment',' For notes v. supra p. 9, n. 6.');"><sup>31</sup></span>