God's name repels the devil

the Prophet (s.a.a.s.) said:
    “The Prophet’s animal tripped,
     so I said,
         `Cursed Satan.’
     The Prophet said
         Do not say, ‘Cursed Satan,’
         for if you say these words,
         Satan becomes arrogant and says,
               ‘With my strength I made him fall.’
         When you say, ‘Bismillah' (in the name of God) 
         Satan will become as small as a fly"


I heard Messenger of God (ﷺ) saying:
    "If a person mentions the Name of God upon entering his house or eating,
     Satan says, addressing his followers:
          'You will find no where to spend the night and no dinner.'
     But if he enters without mentioning the Name of God,
     Satan says;
           'You have found (a place) to spend the night in,
     and if he does not mention the Name of God at the time of eating,
     Satan says:
           'You have found (a place) to spend the night in as well as food."'[Muslim].

When we attended a meal with the Messenger of God (ﷺ),
we would not stretch forth our hands towards the food until he (ﷺ) would start eating first.
Once, we were with him when a little girl rushed in as if someone was impelling her.
She was about to lay her hand on the food when the Messenger of God (ﷺ) caught her hand.
Then a bedouin came in rushing as if someone were pushing him.
He (ﷺ) caught his hand also and said,
    "Satan considers that food lawful for himself on which the Name of God is not mentioned.
     He (Satan) brought this girl to make the food lawful through her but I caught her hand.
     Then he brought the bedouin to make it lawful through him but I caught his hand too.
     By Him in Whose Hand my soul is, now Satan's hand is in my grasp along with their hands."
Then he mentioned the Name of God and began to eat.[Abu Dawud and An-Nasa'i].

Messenger of God (ﷺ) was sitting while a man was eating food.
That man did not mention the Name of God till only a morsel of food was left.
When he raised it to his mouth, he said:
    "Bismillah awwalahu wa akhirahu (in the Name of God, in the beginning and in the end)." Messenger of God (ﷺ) smiled at this and said,
    "Satan had been eating with him
     but when he mentioned the Name of God,
     Satan vomited all that was in his stomach."[Abu Dawud and An-Nasa'i].

So an important lesson can be learnt from the above narrations: Satan will be with us in every deed we do.  However, if we do the deed in the name of God, then Satan will be repelled from doing it.  We often remember to say "bismillah" (in the name of God) before we do a lawful (halaal) good deed (e.g. eating, marital relations, reading Qur'an, etc) to prevent satan from interfering and joining in.  However, who would do a forbidden (haraam) bad deed in the name of God? (If we said "bismillah" before doing a bad deed, we most likely would not do the deed!) 

So remember, when we do a bad deed (e.g. smoking, fornication, corruption, lying, breaking ties of kinship etc) Satan will be doing it with us!  Remember that!  Satan smokes with you, fornicates with you, creates corruption and mischief with you!