Salamu alaykum.
Not so religious-believers will also get less reward than those with strong faith. The punishment they will receive could differ, for some the punishment of the grave will be enough to cleanse them of their sin, however others will be need to enter the hellfire. Also, there is will be bridge over hell into heaven which everyone will need to cross. Those with strong faith, will pass over it in mere seconds. Those with less faith and good deeds will have a longer journey. Those with dwindling faith will have a bridge that weakens and strengths like their faith did. Those with very little faith (but faith nontheless) will have barely enough to keep them up but will make it across. Those who are destined to go to the hellfire will fall in while crossing.
I wish I could provide you with the hadith. I had the chance to buy the whole Bukhari set for a very low price in Saudi Arabia, but for some very strange reason decided not to. I'm kicking myself as we speak.
