"do not return to take it": From here R. Yishmael ruled: An ear of the harvest whose head reaches up to the standing grain — If it were harvested together with the standing grain, it belongs to the owner, (the fact of its being thus harvested indicating it not to have been forgotten), and if not, it belongs to the poor (as shikchah). And if it is in doubt (safek [as to whether it was harvested together with the standing grain]), it belongs to the owner. For the burden of the proof is upon him who would remove it from the owner's domain. And whence is it derived that a safek of leket is leket, a safek of shikchah is shikchah, a safek of peah is peah? From "to the stranger, to the orphan, and to the widow shall it be."