Sahih Bukhari
Beginning of Creation
Volume: 004 / Book Number: 054 / Hadith Number: 493
Narrated 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."