For with God nothing [is or ever] shall be impossible. Luke 1:37 Amplified Bible

the Lord announced to Abraham, “By this time next year, Sarah will give birth to a son,” Sarah overheard and laughed in unbelief. Sarah hears God, predict that she will have a child soon. Given her lifelong barrenness, and the fact that she and her husband were both over 90 years old, her immediate response is to laugh in disbelief. God is calling Sarah and Abraham to believe that He would do a seemingly impossible thing for them.