Dua before marital relations
بِسْمِ الله، اللّهُـمَّ جَنِّبْنا الشَّيْـطانَ، وَجَنِّبِ...
بِسْمِ الله، اللّهُـمَّ جَنِّبْنا الشَّيْـطانَ، وَجَنِّبِ الشَّـيْطانَ ما رَزَقْـتَنا
Bismil-lah, allahumma jannibnash-shaytan, wajannibish-shaytana ma razaqtana
Translation
In the name of Allah. O Allah, keep the devil away from us and keep the devil away from what you have blessed us with.
When to recite
Recited before marital relations. If Allah decrees a child from it, the devil will not harm that child.
Source / Reference
Al-Bukhari 7/99, Muslim 2/1028