Genesis 18:11
Now Abraham and Sarah were old and well stricken in age. As the Creator of all life, there is no barrier to fertility which God cannot overcome with the slightest of thoughts. If a man is impotent or a woman infertile, there is a reason for it. Infertility comes because of sin, age, or injury; or because God has a greater plan. This was the case with Abraham and Sarah. His plan required Isaac to be born under a certain set of circumstances, and it was to God’s greater glory that those circumstances came about in Abraham’s and Sarah’s old age.