The correct original quote should be: Wenn es einen Gott gibt muß er mich um Verzeihung bitten.
It is a quote that supposedly appears on the walls of the cells in the Mauthausen Concentration Camp, according to the documentary they show to people at the camp tours.
From a transcript of the documentary:
In the prison of the camp, called the ‘bunker’, they give lice to prisoners for experiments with pesticides, but the camp’s prison serves primarily to isolate the prisoners.
The camp’s Gestapo wants to extort confessions and holds the prisoners in cells, to beat them bloody, to torture them.
For many this cage is the last stage of life.
While, usually, on the walls of the cells there are writings expressing hope, or testimonies of a wakeful spirit which rebels against bowing down, here we find the last monologue, a sign of discouragement, despair, of imminent death.
"My God why have you forsaken me?
To bend means to lie,
If there is a god, he must ask me forgiveness.”
These writings were found, after 1945.