I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her.” Abraham fell facedown; he laughed and said to himself, “Will a son be born to a man a hundred years old? Will Sarah bear a child at the age of ninety?”
Abraham laughed at that promise God gave him and his wife. It seemed laughable that someone in such old age would be able to have a child. Reading further along in Genesis you find that God keep his promise!
Think about all the promises God has given you! Is your faith full enough to believe that it will come to pass? If not get in the word daily to build you faith and watch God work!
Other scriptures: Hebrews 11:1-2, Hebrews 11:8-12, James 2:26