It was narrated from Ibn `Abbas:
that the Prophet said: "When anyone of you has intercourse with his wife, let him say: Allahumma jannibnish-Shaitana wa jannibish-Shaitana ma razaqtani (O Allah, keep Satan away from me and keep Satan away from that with which You bless me).' Then if they have a child, Allah will never allow Satan to gain control over him or he will never harm him."
English reference: Vol. 3, Book 9, Hadith 1919
Arabic reference: Book 9, Hadith 1994