Answered by Shaykh Yūsuf Badāt
Is it wrong to say ‘rest in peace’ or to give condolences to family members and loved ones of non-Muslims who have just passed away?
Jazāk Allāh Khayr/ Thank you for your question.
Rest in peace is a du’a’ (supplication).
Making du‘ā’ for the disbeliever is permissible with some guidelines.
If the disbeliever is alive, the primary du‘ā’ for such an individual should be that Allāh guide them to the truth. If they have passed on to the next life, then the du‘ā’ should be that Allāh bless them with the best they are entitled to, and worthy of. (See Qur’ānic verse 113 and 114 of chapter 9)
Muftī Muḥammad Shafī (may Allāh’s mercy be upon him) writes,
“When the disbelievers inflicted a wound on the blessed face of the Prophet (peace and blessings upon him) during the battle of Uḥud, he was seen wiping blood from his face and praying, “O Allāh, forgive my people. They do not know”. The object of this prayer of forgiveness for the disbelievers is no other, but that Allāh may bless them with the taufīq (facilitation) of ‘Imān (faith) and Islam, so that they could become deserving of being forgiven. Imām al-Qurṭubī (may Allāh’s mercy be upon him) said, ‘This proves that it is permissible to pray for the forgiveness of a living disbeliever with the intention that this disbelieving person may have the taufīq of Īmān and become deserving of forgiveness” (Ma’ārif al Qur’ān)
And Allāh Knows Best