Is the reward for remembrance (dhikr) recorded for one who sleeps or dies while remembering Allah until he awakens or until the Day of Resurrection, and has this been mentioned in a sound hadith?

There is no hadith indicating that one should sleep while remembering Allah until the soul ascends, but sleeping while remembering Allah is recommended. If a man remembers Allah and then sleeps, an angel will guard him throughout the night. And whoever goes to his bed in a state of purity and remembers Allah until drowsiness overtakes him, no time will pass him by during the night in which he asks Allah for good except that He will grant it to him.