Jesus statements on lust as already having committed adultery.
The Quran doesn't say this explicitly, but there is a notion of inward FASHA. The relationship between inward and outward, is that inward lust leads to the outward, and so if one doesn't cut it off, it will lead to the outward act eventually.
From Misbahal Shariah:
There is nothing more gainful than lowering one's gaze, for the sight is not lowered from things, which Allah has forbidden unless the witnessing of majesty and glory has already come to the heart.
The Commander of the Faithful was asked what could help in lowering one's gaze. He said, 'Submission to the power of Him Who is aware of your secret. The eye is the spy of the hearts and the messenger of the intellect; therefore lower your gaze from whatever is not appropriate to your faith, from whatever your heart dislikes and from whatever your intellect finds repugnant.'
The Holy Prophet said, 'Lower your eyes and you will see wonders.'
Allah said,
قُل لِّلْمُؤْمِنِينَ يَغُضُّوا مِنْ أَبْصَارِهِمْ وَيَحْفَظُوا فُرُوجَهُمْ ذَلِكَ أَزْكَى لَهُمْ إِنَّ اللَّهَ خَبِيرٌ بِمَا يَصْنَعُونَ
Say to the believing men that they cast down their looks and guard their private parts. (
24:30)
‘Isa (‘a) said to the disciples, 'Beware of looking at forbidden things, for that is the seed of desire and leads to deviant behaviour.'
Yahya (‘a) said, 'I would prefer death to a glance which is unnecessary.'
'Abdallah ibn Mas'ud said to a man who had visited a woman while she was ill, 'It would have been better for you to lose your eyes than to have visited your sick person.'
Whenever the eye looks at something forbidden, a knot of desire is tied in the person's heart, and that knot will only be untied by one of two conditions: either by weeping out of grief and regret in true repentance, or by taking possession of what one desired and looked at. And if a person takes possession unjustly, without repentance, then that will take him to the Fire.
As for the one who repents of it with grief and regret, his abode is the Garden and his destiny is Allah's favour.
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So what Nabi Jesus (a) and Imam Jaffar (a) both say about lust, show, also, why thought crimes are crimes. They eventually lead to outward acts. So you have to cut it off and repent before that happens.
