There was a little boy visiting his grandparents on their farm. And he was given a slingshot to play with out in the woods. He practiced in the woods but he could never hit the target. And getting a little discouraged; he headed back to dinner.
As he was walking back he saw Grandma's pet duck. Just out of impulse, he let fly, hit the duck square in the head, and killed it. He was shocked and grieved.

In a panic, he hid the dead duck in the wood pile, only to see his sister watching. Sally had seen it all, but she said nothing.
After lunch that day grandma said, "Sally, let's wash the dishes." But Sally said, "Grandma, Johnny told me he wanted to help in the kitchen today, didn't you Johnny?" And then she whispered to him, "Remember, the duck?"So Johnny did the dishes.  Later Grandpa asked if the children wanted to go fishing, and Grandma said, "I'm sorry but I need Sally to help make supper." But Sally smiled and said, "Well, that's all right because Johnny told me he wanted to help." And she whispered again, "Remember, the duck?" So Sally went fishing and Johnny stayed.

After several days of Johnny doing both his chores and Sally's, he finally couldn't stand it any longer. He came to Grandma and confessed that he killed the duck. She knelt down, gave him a hug, and said, "Sweetheart, I know. You see, I was standing at the window and I saw the whole thing. But because I love you, I forgave you.  But I was just wondering how long would you let Sally make a slave of you." 

I don't know what's in your past. I don't know what one sin the enemy keeps throwing up in your face. But whatever it is, I want you to know something. Jesus Christ was standing at the window. And He saw the whole thing. But because He loves you, He has forgiven you. Perhaps He's wondering how long you'll let the enemy make a slave out of you. The great thing about God is that He not only forgives, but He forgets.

Author unknown