Dua when intending sexual intercouse with your wife

Narrated ibn 'abbas: The Prophet said, "If anyone of you, when intending to have a sexual intercourse with his wife, says:

'Bismillah, Allahumma jannibna-sh-shaitan, wa jannibi-sh-shaitan ma razaqtana'
"In the name of Allah. O Allah! Protect us from Satan and also protect what you bestow upon us"

And if the couple are destined to have a child (out of that very sexual relation), then Satan will never be able to harm that child."

Sahih Bukhari (Book #75, Hadith #397)