Satan can get control over Allah's servants only by whispering to them when they have abandoned their remembrance of Allah, become disdainful, feel complacent when faced with His prohibition, and forget that Allah sees their secret.
Whispering is what comes from outside the heart by tacit permission of the intellect, and is sustained by man's own nature; once it becomes established in the heart, there is error, misguidance, and disbelief. Allah called on His bondsmen with His subtle call and told them about the enmity of Iblis:
Shaytan is an enemy to you, so take him as an enemy. (35:6)
Be with him like a man who, standing near the shepherd's dog, has recourse to the dog's master in order to keep the dog away from him. It is the same when Satan comes to whisper to you, to lead you off the true path and make you forget to remember Allah. Then seek refuge from him with your Lord and his Lord. He will defend the truth against falsehood, and help wronged ones, since He says,
Surely he has no authority over those who believe and who rely on their Lord. (16:99)
Man will only be able to do this if he knows how he comes, and can recognize his methods of whispering, by constant watchfulness, sincerity in the arena of service, awe of the All-Aware, and increased remembrance of Him.
However, anyone who neglects to spend his time in awareness must undoubtedly be the prey of Satan. He should draw a lesson from what Satan does with such a person's self: he leads it to misguidance, deception and haughtiness by duping the person into admiring his own actions, his worship, and his insight.
Satan's insolent behaviour towards him causes a curse to descend on his knowledge, his gnosis and faculty of reasoning for all eternity; yet he has no power over those who are not negligent. Therefore hold to the firmest rope of Allah, which means seeking refuge with Allah, and having a sound need of Allah at every breath. Do not be deceived when Satan makes your acts of obedience appear beautiful in your eye: if he opens ninety-nine doors of goodness for you, it is only so that he may overcome you by opening the hundredth. So meet him with opposition, block his path and reject his charm.