LXX Gen 17:21

ἰτὴν δὲ διαθήκην μου στήσω πρὸς Ἱσαάκ, ὄν τέξεταί σοι Σάρρα εἰς τὸν καιρὸν τοῦτον ἐν τῷ ἐνιαυτῷ τῷ ἑτέρῳ.

But I will establish My covenant with Isaac, whom Sarah will bear to you at this time next year.”