Sahih Bukhari
Beginning of Creation
Volume: 004 / Book Number: 054 / Hadith Number: 503
Narrated Ibn 'Abbas:
The Prophet said, "If anyone of you, on having sexual relation with his wife, says: 'O Allah! Protect me from Satan, and prevent Satan from approaching the offspring you are going to give me,' and if it happens that the lady conceives a child, Satan will neither harm it nor be given power over it."