What is the ruling on publishing "mourning" posts with the noble verse: (Indeed, we belong to Allah, and indeed to Him we will return) written on a black background on social media upon the death of relatives or friends?

Death announcements are of two types: an unlawful type, which is intended to show grief and boast about the deceased's status. This falls under the general prohibition of eulogizing (na'i). The second type, which is lawful, is intended to achieve a legitimate benefit, such as seeking forgiveness for the deceased and attending their funeral, especially if it is meant to inform close relatives. The word "mourning" (haddad) should be avoided in the announcement, and something that encourages seeking forgiveness for the deceased should be placed instead. The announcement should not be in black, but rather should encourage prayers for the deceased. Announcing with "Indeed we belong to Allah, and indeed to Him we will return" is commendable.