EXTRA · Parashas Vayeira · Passuk 18:10
Supplementary classical material; Torah Temimah lists no citation under this passuk.
And he said, “I will surely return to you at this time next year, and behold, a son will be born to Sarah your wife.” And Sarah was listening at the entrance of the tent, which was behind him.
Rashi on Genesis 18:10 (citing Bereishis Rabbah).
Sefaria — Rashi on Genesis 18:10
English: “I will surely return.” The angel was not announcing that he himself would return; rather he spoke as the agent of the Omnipresent. Just as the angel said to Hagar “I will greatly multiply,” though multiplication was not in his power but only as God’s agent, so here he spoke as God’s agent.
Derash on the verse (Rashi / Midrash) — not a formal named middah of the 13. The angel’s wording is read as agency language rather than personal commitment.
When an angel speaks in the first person of a divine act, the words are those of Hashem speaking through His messenger; the promise of Yitzchak’s birth is therefore a direct divine assurance.