The Messenger of Allah ﷺ used to teach us words to say when going to sleep to ward off fear, "In the name of Allah, I seek refuge in the perfect words of Allah from His wrath, His punishment, the evil of His servants, the whisperings of the devils, and from their presence."Abdullah bin Amr used to teach these words to those of his children who had reached an age of understanding, instructing them to say it when going to sleep. As for those who were too young to memorize it, he would write it down for them and hang it around their necks.
حدثنا يزيد أخبرنا محمد بن إسحاق
كان رسول الله ﷺ يعلمنا كلمات نقولهن عند النوم من الفزع بسم الله أعوذ بكلمات الله التامات من غضبه وعقابه وشر عباده ومن همزات الشياطين وأن يحضرون قال فكان عبد الله بن عمرو يعلمها من بلغ من ولده أن يقولها عند نومه ومن كان منهم صغيرا لا يعقل أن يحفظها كتبها له فعلقها في عنقه