10 And He said, "I will certainly return to you according to the time of life, and behold, Sarah your wife shall have a son." (Sarah was listening in the tent door which was behind him.) 11 Now Abraham and Sarah were old, well advanced in age; and Sarah had passed the age of childbearing. 12 Therefore Sarah laughed within herself, saying, "After I have grown old, shall I have pleasure, my lord being old also?"
Matthew Henry's Commentary on Genesis 18:10-12
Commentary on Genesis 18:9-15
(Read Genesis 18:9-15)
Where is Sarah thy wife? was asked. Note the answer, In the tent. Just at hand, in her proper place, occupied in her household concerns. There is nothing got by gadding. Those are most likely to receive comfort from God and his promises, who are in their proper place, and in the way of their duty, 17; but He who searches the heart, saw that the one sprung from unbelief, and the other from faith. She denied that she had laughed. One sin commonly brings in another, and it is not likely we shall strictly keep to truth, when we question the Divine truth. But whom the Lord loves he will rebuke, convict, silence, and bring to repentance, and if they sin before him.