While sleeping you can recite verse 9 of Surah An-Nabar. The verse is: وََّجَعَلۡنَا نَوۡمَكُمۡ سُبَاتًا pronunciation : That is , I have rested your sleep. Also , while sleeping you can recite this prayer "Allahumma bismika amutu wa ahiya". Because the Prophet (peace be upon him) himself used to recite this prayer while sleeping. It is narrated from Hazrat Huzaifah (R) that he said that the Prophet (SAW) used to say while sleeping: "Allahumma biismika amutu wa ahiya" (meaning: O Allah! [Sunan Abu Daud , Hadith No. 5049 , Hadith Manah Sahih].