According to the Time of Life

Genesis 18:1-2

And the LORD appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day; And he lift up his eyes and looked, and, lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground...

Genesis 18:9-15

And they said unto him, Where is Sarah thy wife?

And he said, Behold, in the tent.

And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son.

And Sarah heard it in the tent door, which was behind him.

Now Abraham and Sarah were old and well stricken in age; and it ceased to be with Sarah after the manner of women.

Therefore Sarah laughed within herself, saying, After I am waxed old shall I have pleasure, my lord being old also?

And the LORD said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old? Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son.

Then Sarah denied, saying, I laughed not; for she was afraid.

And he said, Nay; but thou didst laugh.