God rest soul
(God) rest his/her/their soul
May this person find peace in the afterlife. My dear father, God rest his soul, worked his whole life so that we would have the opportunities he never had growing up. My grandmother was only 59 when she passed, rest her soul.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
God rest someone's soul.
May God bless a previously mentioned person who has died. I remember what my mother, God rest her soul, used to say about that.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.