TT #605 · Parashas Ki Seitzei · Sixth / Seventh Aliyah · Passuk 24:20
When you beat your olive tree, you shall not go over the boughs again; it shall be for the stranger, the orphan, and the widow.
Torah Temimah points to Sifrei Devarim 284 / Hullin.
TT lemma: כִּי תַחְבֹּט זֵיתְךָ.
Sefaria — Sifrei Devarim 284 / Hullin
English: ‘When you beat your olive tree’ – at the time of the beating.
Derash on the timing of the command (Sifrei) — the prohibition applies during the harvest act itself.
When olives are harvested by beating the tree, one may not return afterward to take what remains; that remainder is for the poor.