Sunan Ibn Majah Book 9, Hadith 1919

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 - ‏"‏ ‏.‏

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.”