Isti`adhah means, "I Seek Refuge with Allah from the cursed Satan so that he is prevented from affecting my religious or worldly affairs, or hindering me from adhering to what I was commanded, or luring me into what I was prohibited from.'' Indeed, only Allah is able to prevent the evil of Satan from touching the son of Adam. This is why Allah allowed us to be lenient and kind with the human devil, so that his soft nature might cause him to refrain from the evil he is indulging in. However, Allah required us to seek refuge with Him from the evil of Satan, because he neither accepts bribes nor does kindness affect him, for he is pure evil. Thus, only He Who created Satan is able to stop his evil. This meaning is reiterated in only three Ayat in the Qur'an. Allah said in Surat Al-A`raf,
﴿ خُذِ ٱلۡعَفۡوَ وَأۡمُرۡ بِٱلۡعُرۡفِ وَأَعۡرِضۡ عَنِ ٱلۡجَـٰهِلِينَ ﴾
(Show forgiveness, enjoin what is good, and turn away from the foolish (i.e. don't punish them).) (7:199)
This is about dealing with human beings. He then said in the same Surah,
﴿ وَإِمَّا يَنزَغَنَّكَ مِنَ ٱلشَّيۡطَـٰنِ نَزۡغٌ۬ فَٱسۡتَعِذۡ بِٱللَّهِۚ إِنَّهُ ۥ سَمِيعٌ عَلِيمٌ ﴾
(And if an evil whisper comes to you from Shaytan, then seek refuge with Allah. Verily, He is Hearing, Knowing (7: 200).)
Allah also said in Surat Al-Mu'minun,
﴿ ٱدۡفَعۡ بِٱلَّتِى هِىَ أَحۡسَنُ ٱلسَّيِّئَةَۚ نَحۡنُ أَعۡلَمُ بِمَا يَصِفُونَ • وَقُل رَّبِّ أَعُوذُ بِكَ مِنۡ هَمَزَٲتِ ٱلشَّيَـٰطِينِ • وَأَعُوذُ بِكَ رَبِّ أَن يَحۡضُرُونِ ﴾
(Repel evil with that which is better. We are Best-Acquainted with the things they utter. And say: "My Lord! I seek refuge with You from the whisperings (suggestions) of the Shayatin (devils). And I seek refuge with You, My Lord! lest they should come near me.'' (23:96-98).)
Further, Allah said in Surat As-Sajdah,
﴿ وَلَا تَسۡتَوِى ٱلۡحَسَنَةُ وَلَا ٱلسَّيِّئَةُۚ ٱدۡفَعۡ بِٱلَّتِى هِىَ أَحۡسَنُ فَإِذَا ٱلَّذِى بَيۡنَكَ وَبَيۡنَهُ ۥ عَدَٲوَةٌ۬ كَأَنَّهُ ۥ وَلِىٌّ حَمِيمٌ۬ • وَمَا يُلَقَّٮٰهَآ إِلَّا ٱلَّذِينَ صَبَرُواْ وَمَا يُلَقَّٮٰهَآ إِلَّا ذُو حَظٍّ عَظِيمٍ۬ • وَإِمَّا يَنزَغَنَّكَ مِنَ ٱلشَّيۡطَـٰنِ نَزۡغٌ۬ فَٱسۡتَعِذۡ بِٱللَّهِۖ إِنَّهُ ۥ هُوَ ٱلسَّمِيعُ ٱلۡعَلِيمُ ﴾
In the Arabic language, Shaytan is derived from Shatana, which means the far thing. Hence, the Shaytan has a different nature than mankind, and his sinful ways are far away from every type of righteousness. It was also said that Shaytan is derived from Shata, (literally `burned'), because it was created from fire. Some scholars said that both meanings are correct, although they state that the first meaning is more plausible. Further, Siybawayh (the renowned Arab linguistic) said, "The Arabs say, `So-and-so has Tashaytan,' when he commits the act of the devils. If Shaytan was derived from Shata, they would have said, Tashayyata (rather than Tashaytan).'' Hence, Shaytan is derived from the word that means, far away. This is why they call those who are rebellious (or mischievous) from among the Jinns and mankind a `Shaytan'. Allah said,
﴿ وَكَذَٲلِكَ جَعَلۡنَا لِكُلِّ نَبِىٍّ عَدُوًّ۬ا شَيَـٰطِينَ ٱلۡإِنسِ وَٱلۡجِنِّ يُوحِى بَعۡضُهُمۡ إِلَىٰ بَعۡضٍ۬ زُخۡرُفَ ٱلۡقَوۡلِ غُرُورً۬اۚ ﴾
(And so We have appointed for every Prophet enemies ـ Shayatin (devils) among mankind and Jinn, inspiring one another with adorned speech as a delusion (or by way of deception)) (6:112).
In addition, the Musnad by Imam Ahmad records that Abu Dharr said that the Messenger of Allah said,
« يَا أَبَا ذَرَ تَعَوَّذْ بِاللهِ مِنْ شَيَاطِينِ الْإِنْسِ وَالْجِنِّ »
(O Abu Dharr! Seek refuge with Allah from the devils of mankind and the Jinns.) Abu Dharr said, "I asked him, `Are there human devils' He said, (Yes.)'' Furthermore, it is recorded in Sahih Muslim that Abu Dharr said that the Messenger of Allah said,
« يَقْطَعُ الصَّلَاةَ الْمَرْأَةُ وَالْحِمَارُ وَالْكَلْبُ الْأَسْوَدُ »
(The woman, the donkey and the black dog interrupt the prayer (if they pass in front of those who do not pray behind a Sutrah, i.e. a barrier).) Abu Dharr said, "I said, `What is the difference between the black dog and the red or yellow dog? He said,
« الْكَلْبُ الْأَسْوَدُ شَيْطَانٌ »
(The black dog is a devil.).''
Also, Ibn Jarir At-Tabari recorded that `Umar bin Al-Khattab once rode a Berthawn (huge camel) which started to proceed arrogantly. `Umar kept striking the animal, but the animal kept walking in an arrogant manner. `Umar dismounted the animal and said, "By Allah! You have carried me on a Shaytan. I did not come down from it until after I had felt something strange in my heart.'' This Hadith has an authentic chain of narrators. 
