Sahih Al Bukhari – Book of Beginning Of Creation
Volumn 004, Book 054, Hadith Number 493.
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Narated By Ibn 'Abbas : The Prophet said, "If anyone of you, when having sexual relation with his wife, say: 'In the name of Allah. O Allah! Protect us from Satan and prevent Satan from approaching our offspring you are going to give us,' and if he begets a child (as a result of that relation) Satan will not harm it."