I know of a few early church writings that can be understood as saying we go to heaven when we die. But that is not what I'm asking. Rather, I'm looking for the first known case (post NT) where, in the context of consoling those left behind, we are told the deceased is in heaven.
For example, when Paul was reassuring the Thessalonians about those that died before Jesus returned in 1 Thess. 4:13-18 he points them to Christ's second coming and the resurrection.
Said a different way, when did the emphasis on the deceased being in heaven now, rather than their future resurrection, become the message given to those that remain with the intention to give them hope and peace? When do we first see the initial response to grief being "he's at peace in heaven now" rather than "he will be raised again"?
I am representing this as a shift, or change of emphasis, simply due to my research showing the resurrection to be the common response at the time of the NT: 1 Thess 4, 1 Cor. 15, John 11. Regardless how you read those passages, the question remains, when was the emphasis explicitly first placed on heaven. Again, it must be in this context. Not just speaking generally on what happens after death, or even the author speaking of his own death, but when the author is consoling others.