  We report the structure, magnetic, and thermal property measurements on
single crystalline and polycrystalline samples of Ru substituted honeycomb
lattice iridate Na$_2$Ir$_x$Ru$_{1-x}$O$_3$ (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3,
0.5). The evolution of magnetism in Na$_2$Ir$_x$Ru$_{1-x}$O$_3$ has been
studied using dc and ac magnetic susceptibility, and heat capacity
measurements. The parent compound Na$_2$IrO$_3$ is a spin-orbit driven Mott
insulator with magnetic order of reduced moments below $T_N =<EMAIL_ADDRESS>In the
Ru substituted samples the antiferromagnetic long range state is replaced by a
spin glass like state even for the smallest substitution suggesting that the
magnetic order in Na$_2$IrO$_3$ is extremely fragile. We argue that these
behaviors indicate the importance of nearest-neighbor magnetic exchange in the
parent Na$_2$IrO$_3$. Additionally, all samples show insulating electrical
transport.
