A.T. Robertson Commentary Hebrews 11:18

"even he to whom it was said, In Isaac shall thy seed be called:" — Hebrews 11:18 (ASV)

To whom it was said (προς ελαληθη). First aorist passive indicative of λαλεω (Genesis 21:12). God's very words were in the heart of Abraham now about Isaac "his only son" (τον μονογενη. Cf. Luke 7:12).