Where does the increase in mass come from in fission?

[Ciaran H]

If energy is released during nuclear fission, why is the mass of the products (the two new nuclei and fission neutrons) greater than the mass of the original nuclei? In accordance to E=mc^2, shouldn't the release of energy result in the products having a lesser mass than the original nuclei?

 

[Bandersnatch]

why is the mass of the products (the two new nuclei and fission neutrons) greater than the mass of the original nuclei?

It isn't. It's lower. Try counting masses in e.g.:
n + U235 -> 3n + Ba141 + Kr92
What do you get?