I'll let Dan Barker explain it. He had been debating with an Islamic scholar, Hussanain Rajabali, who had stated that Allah is a "just" god as well as an "infinitely merciful" god. Oops!
"Justice means that punishment is administered with the exact amount of severity that is deserved for the crime that is committed. We don’t put children in prison for stealing cookies, and we don’t merely fine a murderer $50. Mercy, on the other hand, means that punishment is administered with less severity than deserved. When the police officer lets you off with a warning instead of a ticket for breaking the speed limit, that is mercy. If God is infinitely merciful, he can never be just. If God is ever just (not to mention infinitely just), then he cannot be infinitely merciful. A God who is both infinitely merciful and just not only does not exist, he cannot exist. This is one of the positive arguments for the nonexistence of God based on incompatible properties (or incoherency). If God is defined as a married bachelor, we don’t need to discuss evidence or argument; we can simply claim a logical impossibility."
"[If] God is infinitely merciful, then I cannot go to hell. It wouldn’t matter how I lived or what I thought, infinite mercy would absolve me of any crime, no matter how great, including the crime of refusing to believe in God, accept his authority or admit that I had done anything wrong."
Barker, Dan (2009-05-01).
Godless: How an Evangelical Preacher Became One of America's Leading Atheists (p. 79-80).
Perseus Books Group. Kindle Edition.
An exquisite example there of how religions require their followers to hold two or more mutually exclusive views simultaneously, like the belief in an omniscient god and free will. Don't you just love it when those simple little arrows of irrefutable logic hit home like an Exocet and destroy centuries of unthinking dogma? What could mankind have achieved if ignorant superstition hadn't been allowed to hijack our cultures and condition our thinking, replacing reason and logic with dogmas and knee-jerk reflexes, just to provide an easy living for a parasitic class of religious clerics?
What a waste of two thousand years!
So Muslims, is Allah just or is Allah infinitely merciful, and how did Mohammed get it wrong about the other one?
If Allah is infinitely merciful, why does it make any difference how you conduct yourself or what you believe?
Christians and other theists, before you rejoice at the discomfort of those you hate, you might like to consider helping Muslims out here, because this argument comprehensively refutes your god too, unless you want to tell me your god isn't "just" or isn't "merciful".