Long ago, there used to live a very great King by the name Nruga, the son of Ikshvaaku. He gave as many goodaanams as there are grains of sand on the earth, stars in the heavens, or drops in a rain shower. He gave the best quality kapila varna cows, decorated with pure golden hooves and horns, along with their calves. He gave them to the most learned braahmanas, whose families were in need, were young and possessed of excellent character and qualities, who were dedicated to truth, famous for their austerity, vastly learned in the Vedic scriptures and saintly in their behaviour. He performed many other such great daanams for the needy. In addition, he performed many yagnyas and executed various pious welfare activities.
Once, a cow owned by a learned braahmana wandered away and entered the herd being given as daanam by Nruga. Unaware that he was giving a cow that did not belong to him, he gave it to one other needy braahmana. When the owner of the cow saw his cow being taken away, he said "The cow belongs to me!" and the other said "No! It was given to me by Nruga." Nruga comes to know about this and offers each one of them a thousand cows of highest quality and asked them to save him from this difficult situation. However, both the braahmanas go away leaving the cow.
Yamadharmaraaja, after King Nruga leaves his physical body and comes to Yamaloka, asks Nruga "do you wish to experience the results of your paapam first, or those of your punya? Indeed, I see no end to the greatest daanams you have performed, or to your consequent enjoyment in the urdhva lokas. However, you made the sin of stealing a cow from a braahmana". Nruga chooses to face the consequences of his paapam first and immediately falls as a huge chameleon in a well. Since he always had bhakti towards the Lord and performed uncountable number of great daanams, he always remembered who he was, and what mistake he committed. He used to repent for his mistake and spent a very long time alone in the well, always doing Bhagavat-dhyaanam.
After a very long time, once when Shri Krishna, Saamba, Pradyumna, Chaaru, Bhaanu, Gada and other boys were playing, out of thrist they goto the well where Nruga was living. Out of pity, Shri Krishna takes him out of the well. The touch of the Lord of the universe made Nruga get a divya tejaswi form, with radiating kiritam and ornaments and tejas of Sun. On being asked by Shri Krishna, the Sarvagnya, the reason for the chameleon form, Nruga tells him his unfortunate story. He does a stotram to Lord krishna, does a pradakshinam, takes leave from the Lord and before the eyes of everyone flies to urdhva lokas in a divya vimaanam.
Morals in the Story:
1. Even for a great person like Nruga, one mistake, which he did unknowingly, made him experience the result of his paapam. Thus one should be very careful not to commit any kind of sin even unknowingly and lead a very ideal life.
2. Some or the other time, one must experience the results of his paapa or punya. However, if one surrenders himself to the God, He will lift you from the samsaaram and in the end give you kaivalyam, as Krishna did to Nruga.
3. Since Nruga never forgot remembering the Lord and the Lord was impressed by his great acts, Krishna granted him urdhva lokas in the end. So the end result for a good person will always be good.
Moral Stories 
very insightful read, thankyou.