It is not permissible to describe the Deceased as being forgiven or the recipient of mercy

All praise is due to Allâh and may blessings and peace be upon His servant and Messenger, our Prophet Muhammad, and upon his family and Companions. To proceed:

The announcements in the newspapers have become numerous concerning the deaths of some of the people and so has the publishing of condolences of the relatives of those who have passed. In these writings, the people describe the deceased as being 'forgiven' or 'the recipient of mercy' or phrases similar to that which suggest the person being from the people of Paradise. It is not unknown to every person who is familiar with the matters of Islam and its creed of beliefs that this is from the matters that no one knows but Allâh. It is also known that the creed of Ahlus-Sunnah wal-Jama'ah is that it is not permissible to testify that anyone will definitely be in Paradise or the Fire. The only exception to this is whoever has been given this confirma- tion in the Noble Qur'an, like Abu Lahab, or whoever the Messenger testified for, like the Ten among the Companions who were given the tidings of Paradise and others like them. The likes of such phrases carry the meaning of a testimony for the person that he is forgiven or is the recipient of mercy. For this reason, what should be said instead of these phrases is 'May Allâh forgive him' or 'May Allâh have mercy on him' or similar statements from the words of supplications for the deceased. I ask Allah, Who is far exalted above any shortcomings, to guide us all to the right path. May Allâh send blessings upon our Prophet Muhammad, his family and his Companions.

Source:
Ash-Shaykh 'Abdul-'Aziz bin 'Abdullah bin Baz
Fatawa Islamiyah, Vol. 3 Pages 129-130