The distinction to be made here is this: there is a difference between contemplating a deed and intending it.
“Contemplation” may be unaccompanied by any outward action; in that case, it incurs no punishment whatsoever. Indeed, if a person abandons it for Allah’s sake, as Joseph abandoned what he had contemplated, he is rewarded for doing so, just as Joseph was rewarded. Hence Ahmad said, “Contemplation is of two kinds: passing thoughts and persistent resolve.”
Thus, the Quran indicates that Joseph committed no sin whatsoever in this affair. Rather, Allah turned evil and indecency away from him, for he was one of His chosen servants. This was despite the attempts to seduce him, the lies, the enlistment of the women against him, his imprisonment, and the other circumstances under which scarcely any human being could patiently refrain from sexual immorality. Yet Joseph feared Allah and remained patient, so Allah, in His mercy, rewarded him in this world.
“And the reward of the Hereafter is better for those who believe and are mindful of Allah.”
As for “firm intention,” when a person has the ability to act, it must be accompanied by whatever action lies within his power—even a glance, a movement of the head, a word, a step, or a bodily movement. This clarifies the meaning of the Prophet’s saying, may Allah bless him and grant him peace:
“When two Muslims confront one another with their swords, both the killer and the one killed are in the Fire.”
The one killed intended to kill his opponent and fought as best he could, but was unable to achieve his aim. The same applies to the man who said, “If I had wealth like so-and-so, I would use it as he does.” He intended to do what lay within his power, namely speaking, but was unable to do that (*).
Likewise, whoever calls others to misguidance bears a burden of sin equal to that of those who follow him, without their burdens being diminished in the least. This is because he intended their misguidance and did what lay within his power by calling them to it, since that alone was within his power.