Genesis 18:10
“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.”
KJV
Read in Genesis 18Meaning
The visitor announces that he will return at the appointed time and that Sarah will then have a son; Sarah hears from the tent entrance.
Read carefully
This is a particular promise within the Abraham-Sarah story, not a general guarantee that every hoped-for pregnancy will occur through miraculous intervention.
Reflection
The verse brings timing and identity together: the promised child is to come through Sarah, despite circumstances that appear impossible.