EXTRA · Parashas Vayeira · Passuk 21:2
Supplementary classical material; Torah Temimah lists no citation under this passuk.
Sarah conceived and bore Avraham a son in his old age, at the appointed time of which God had spoken to him.
Rashi on Genesis 21:2.
Sefaria — Rashi on Genesis 21:2
English: “At the appointed time of which He had spoken to him.” He fixed the time when He said “at the appointed time I will return to you”: He scratched a mark on the wall and said to him, “When the sun reaches this mark next year, she will give birth.”
Derash on the verse (Rashi) — not a formal named middah of the 13. The earlier promise is read as a dated commitment verified by the birth.
Divine promises of a fixed time are kept to the mark; the birth of Yitzchak confirms the exact calendar spoken a year earlier.