A good son-in-law is like the acquisition of a new son; a bad one is like the loss of your daughter. (Jewish Proverb)
You reproach your daughter, but you mean your daughter-in-law. (Jewish Proverb)
With a good son-in-law you gain a son, with a bad one you lose your daughter, too. (Jewish Proverb)
One of life's greatest mysteries is how the boy who wasn't good enough to marry your daughter can be the father of the smartest grandchild in the world. (Jewish Proverb)