Reference for Bava Metzia 235:18

מאי לאו בהא קמיפלגי דת"ק סבר הבטה בהפקר קני ואי יהיבי ליה אגרא אין ואי לא לא ורבי יוסי סבר הבטה בהפקר לא קני וכי אזלי צבור ומייתי השתא הוא דקא זכי ביה

— But, said R. Nahman, there is no difficulty: here [in the Mishnah] the reference is to lifting up; there, to watching.<span class="x" onmousemove="('comment',' Lit., 'looking'. In both instances the reference is to hefker. But if the labourer was engaged to tie sheaves, thus having to lift them up, his employer acquires title to them, and therefore must pay him. But if his work was to keep guard, the mere watching does not effect possession, and therefore his employer can force him to accept them as his wages. ');">¹⁴</span>

Jastrow