What to say to foil the devil's plots
 

أَعُوذُ بكَلِمَاتِ اللهِ التَّامَّاتِ الَّتِي لَا يُجَاوِزُهُنَّ بَرٌّ وَلاَ فَاجرٌ مِنْ شّرِّ مَا خَلقَ، وبَرَأَ وذَرَأَ، ومِنْ شَرِّ مَا يَنْزِلُ مِنَ السَّمَاءِ وِمنْ شَرِّ مَا يَعْرُجُ فيهَا، ومِن شَرِّ مَا ذَرَأَ في الأَرْضِ ومِنْ شَرِّ مَا يَخْرُجُ مِنْهَا، وِمنْ شَرِّ فِتَنِ اللَّيْلِ والنَّهارِ، ومِنْ شَرِّ كُلِّ طارِقٍ إِلَّا طَارِقاً يَطْرُقُ بخَيْرٍ يَا رَحْمَنُ

247. 'A'oothu bikalimaatil-laahit-taammaatil-latee laa yujaawizuhunna barrun wa laa faajimn min sharri maa khalaqa, wa bara'a wa thara'a, wa min sharri maa yanzilu minas-samaa'i, wa min sharri maa ya'ruju feehaa, wa min sharri maa thara'a fil-'ardhi, wa min sharri ma yakhruju minhaa, wa min sharri fitanil-layli wannahaari, wa min sharri kulli taariqin 'illaa taariqan yatruqu bikhayrin yaa Rahmaan.

I seek refuge in the Perfect Words of Allah -which neither the upright nor the corrupt may overcome - from the evil of what He created, of what He made, and of what He scattered, from the evil of what descends from the heavens, and of what rises up to them, from the evil of what He scattered in the earth and of what emerges from it, from the evil trials of night and day, and from the evil of every night visitor, except the night visitor who comes with good. O Merciful One.

Reference: Ahmad 3/419, with an authentic chain of narration, and Ibn As-Sunni (no. 637). Al-Arna'ut, graded its chain authentic in his checking of Al-'Aqidah At-Tahawiyyah p. 133. See also Majma'uz-Zawa'id, 10/127.