Clown knifes are too delicate and african cichlids are too aggressive. You'll wind up with a dead clown. You might be able to manage if you try the most peaceful africans possible (Pseudotropheus sp., Labidochromis caeruleus, Iodotropheus sprengerae), but I assume you already have the tank stocked.
Why would I say this? Well, I have a saulosi in with my community tank right now--don't ask why--and it hasn't attacked anything. The problem is I have no idea how the temperament would be with pairs or groups.