Sunan Ibn Majah 1919
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.”
حَدَّثَنَا عَمْرُو بْنُ رَافِعٍ، حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ سَالِمِ بْنِ أَبِي الْجَعْدِ، عَنْ كُرَيْبٍ، عَنِ ابْنِ عَبَّاسٍ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ ‏
"‏ لَوْ أَنَّ أَحَدَكُمْ إِذَا أَتَى امْرَأَتَهُ قَالَ اللَّهُمَّ جَنِّبْنِي الشَّيْطَانَ وَجَنِّبِ الشَّيْطَانَ مَا رَزَقْتَنِي ثُمَّ كَانَ بَيْنَهُمَا وَلَدٌ لَمْ يُسَلِّطِ اللَّهُ عَلَيْهِ الشَّيْطَانَ - أَوْ لَمْ يَضُرَّهُ - ‏"‏ ‏.‏