References in classic literature ?
When I got up to my little room and said my prayers, I did not forget Joe's recommendation, and yet my young mind was in that disturbed and unthankful state, that I thought long after I laid me down, how common Estella would consider Joe, a mere blacksmith: how thick his boots, and how coarse his hands.
You're very good to say so, sir, and I'm not unthankful.
Then you are an ungrateful, unworthy, demd unthankful little fairy,' said Mr Mantalini.
Then I reproached myself with my unthankful temper, and that I had repined at my solitary condition; and now what would I give to be on shore there again
One of the most important methods satan uses to reach this evil goal is the prevent people from seeing the best in everything that happens, and thus make them rebellious and unthankful towards Allah.