Will a man be held accountable for wishing to commit a sin—such as adultery—if he does not commit it for some reason?

Wishing to commit a sin, if it is merely a fleeting thought, is forgiven. However, if one resolves to commit it but then abandons it for the sake of Allah, a good deed is recorded for them.

But if one resolves to commit it and is unable to do so, they are punished with the punishment of the one who commits it, like someone who meets their companion with their sword, eager to kill them. Both of them are in the Hellfire, according to the Prophet's (peace and blessings be upon him) narration: "If two Muslims meet with their swords, then both the killer and the killed are in the Hellfire." It was asked, "O Messenger of Allah, this is the killer, but what about the killed?" He replied, "He was eager to kill his companion."

Shaykh al-Islam Ibn Taymiyyah holds the view that a firm intention, when accompanied by the ability to carry out the act, makes its possessor liable to the punishment of the one who commits the act. This is because such a firm intention is not merely a passing thought, nor just a resolve for a future action, but rather it is accompanied by preliminary steps towards the intended action, such as looking with lust in adultery and walking towards it, or approaching stolen money in theft.