Dua before sleeping — Ayat al-Kursi
اللهُ لاَ إِلَهَ إِلاَّ هُوَ الْحَيُّ...
اللهُ لاَ إِلَهَ إِلاَّ هُوَ الْحَيُّ الْقَيُّومُ...
Allahu la ilaha illa huwal-hayyul-qayyoom... (Ayat al-Kursi — 2:255)
Translation
Recite Ayat al-Kursi (2:255) before sleeping. Whoever recites it, Allah will appoint a guardian angel to protect them and Satan will not come near them until morning.
When to recite
Recited before sleeping. One of the most powerful protective recitations.
Source / Reference
Al-Bukhari 4/487