Given an example of two matrices A and B such that

Given an example of two matrices $A$ and $B$ such that

$\mathrm{A} \neq \mathrm{O}, \mathrm{B} \neq \mathrm{O}, \mathrm{AB}=\mathrm{O}$ and $\mathrm{BA} \neq \mathrm{O}$