Jami` at-Tirmidhi 3528
`Amr bin Shu`aib narrated from his father, from his grandfather, that the Messenger of Allah (ﷺ) said:
“When one of you becomes frightened during sleep, then let him say: ‘I seek refuge in Allah’s Perfect Words from His anger, His punishment, and the evil of His creatures, from the whisperings of the Shayatin, and that they should come (A`ūdhu bikalimātillāhit-tāmmati min ghaḍabihī wa `iqābihī wa sharri `ibādih, wa min hamazātish-shayāṭīni wa an yaḥḍurūn).’ For verily, they shall not harm him.” He said: “So `Abdullah bin `Amr used to teach it to those of his children who attained maturity, and those of them who did  not, he would write it on a sheet and then hang it around his neck.”
حَدَّثَنَا عَلِيُّ بْنُ حُجْرٍ، حَدَّثَنَا إِسْمَاعِيلُ بْنُ عَيَّاشٍ، عَنْ مُحَمَّدِ بْنِ إِسْحَاقَ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏
"‏ إِذَا فَزِعَ أَحَدُكُمْ فِي النَّوْمِ فَلْيَقُلْ أَعُوذُ بِكَلِمَاتِ اللَّهِ التَّامَّةِ مِنْ غَضَبِهِ وَعِقَابِهِ وَشَرِّ عِبَادِهِ وَمِنْ هَمَزَاتِ الشَّيَاطِينِ وَأَنْ يَحْضُرُونِ ‏.‏ فَإِنَّهَا لَنْ تَضُرَّهُ ‏"‏ ‏.‏ قَالَ وَكَانَ عَبْدُ اللَّهِ بْنُ عَمْرٍو يُلَقِّنُهَا مَنْ بَلَغَ مِنْ وَلَدِهِ وَمَنْ لَمْ يَبْلُغْ مِنْهُمْ كَتَبَهَا فِي صَكٍّ ثُمَّ عَلَّقَهَا فِي عُنُقِهِ ‏.‏ قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ ‏.‏