First: what the Lawgiver has forbidden and the wronged person finds objectionable.

Second: what the Lawgiver has forbidden, even if the wronged person does not object to it, such as unlawful sexual intercourse and gambling.

Third: what the person concerned finds objectionable but the Lawgiver has permitted. This is not injustice.

Fourth: what neither the person concerned nor the Lawgiver disapproves of.

The Lawgiver forbids something to which the person concerned consents only when it constitutes injustice. A person is ignorant of his own best interests and may consent to something without knowing that it entails harm to him—harm that he does not deserve. Thus, once the true situation becomes clear to him, he no longer consents. Hence Tāwūs said: “Whenever two men come together for anything other than Allah’s sake, they part hating one another.”

A man who has illicit intercourse with a woman or a boy commits both injustice and an indecency if he has coerced her. If she has willingly consented to him, this is an indecency, and it also involves wronging the other person: by consenting, each has helped the other harm himself. This is especially so if one of them was the one who invited the other to commit the indecency, for he has actively sought to wrong and harm the other. Indeed, even if he were to tell him to commit a sin from which he himself stood to gain nothing, he would be wronging him. That is why he bears some of the burdens of sin of whomever he leads astray without knowledge. How much more so, then, if he seeks to obtain his own gratification from the other while harming him?