When Yangshan was residing at Dongping, a letter and a mirror arrived from Guishan. Yangshan ascended the high seat and received the letter. Then, holding up the mirror, he addressed the assembly.
"Monks, this mirror comes from Guishan. Tell me, is it Guishan's mirror or is it mine? If you say it's mine, still it was sent by Guishan. If you say it's Guishan's, still it's here in my hands. If you can say something, I'll save the mirror; if you can't, I'll smash it."
He repeated this three times, but no one in the assembly responded. Yangshan then smashed the mirror.
Later, Wuzu Shijie answered in place of the assembly: "I would have said, 'Teacher, please, try to explain your meaning a bit more clearly,' then snatched away the mirror and shattered it myself."
-from Entangling Vines, Thomas Yuho Kirchner (trans)