For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.

And she conceived and bore a son in her old age, at the time that God had foretold her.

And Sarah conceived, and bore Abraham a son in his old age, at the appointed time of which God had spoken to him.

and Sarah conceiveth, and beareth a son to Abraham, to his old age, at the appointed time that God hath spoken of with him;

And Sarah became with child, and gave Abraham a son when he was old, at the time named by God.

And she conceived and gave birth to a son in her old age, at the time that God had foretold to her.

Itaque concepit et peperit Sarah ipsi Abraham filium in senectute ejus, in tempore quod illi dixerat Deus.

She bare Abraham a son. This is said according to the accustomed manner of speaking; because the woman is neither the head of a family, nor brings forth properly for herself, but for her husband. What follows, however, is more worthy of notice, In his old age, at the set time, which God had predicted: for the old age of Abraham does, not a little, illustrate the glory of the miracle. And now Moses, for the third time, recalls us to the word of God, that the constancy of his truth may always be present to our minds. And though the time had been predicted, alike to Abraham and to his wife, yet this honor is expressly attributed to the holy man; because the promise had been especially given on his account. Both, however, are distinctly mentioned in the context.

For Sarah conceived, and bare Abraham a son in his (a) old age, at the set time of which God had spoken to him.
(a) Therefore the miracle was greater.

For Sarah conceived,.... This explains what is meant by the Lord's visiting her, and doing to her according to his word, see Hebrews 11:11,
and bare Abraham a son in his old age; which circumstance is remarked, that the favour might appear the greater, and the more wonderful; or, "unto", or "for his old age" (n), for the comfort of him in his old age, who having lived so many years under the promise of a son, and in the expectation of one, even of the promised seed, from whom the Messiah should spring, now has one, than which nothing could yield him greater consolation:
at the set time of which God had spoken to him, Genesis 17:21; God was not only faithful in fulfilling his promise, but in keeping the exact time of it.
(n) "pro senectute ejus", Vatablus; "senectuti ejus", Junius & Tremellius.

Sarah conceived - Sarah by faith, received strength to conceive, Hebrews 11:11. God therefore, by promise, gave that strength. Abraham was old, and Sarah old, and both as good as dead, and then the word of God took place.