Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
The sleep of the dead in a dream indicates their comfort in the Hereafter.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
Whoever sees a dead person sleeping is heedless of praying for them and giving charity on their behalf.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
The sleep of the dead indicates their good state and safety from torment.