Ibn Al Hasan (A.R.) once remarked: “I am grieving for forty years over a sin committed by me.” Someone enquired, “What sin is that which has caused great concern and grief in you?”
He replied, “Once I was visited by a friend and in order to entertain him, I bought fish which we subsequently ate. After the meal, I scraped some sand from my neighbour’s wall without his permission, to wash my hands. I am still crying over that sin.”
The questioner expressed surprise over the fact that such a small fault has created so much of anguish and concern. So Ibn Al Hasana explained that according to the Prophet (peace and blessing upon him) the biggest sin before Allah is that little slip or error which man regards as trifle and unimportant and therefore thinks it unnecessary to seek forgiveness.
On the other hand, if he acknoweldges his wrongs considering them to be quite serious, he would certainly feel guilty and ashamed of his actions and this would induce him to repent, seek Allah’s forgiveness through which he receives pardon and in this way obliterates all trace of the sin.
Source: Death by Husainiyah Publications