Daman Hongren (601-674 AD) was the Fifth Patriarch of Zen in China.
When he was dying and it was time to choose a successor to run his monastery, he set a task for those who aspired to the position. Each would submit a short poem to demonstrate their grasp of the teachings of Zen. The Chief Disciple, Shenxiu, was popularly regarded as the favoured candidate and no-one bothered to challenge him. He wrote on a wall:

The mind is a mirror
Which becomes dusty and unclear
Clean off the dust and
Experience the Truth

 

It stood alone for some days, until another disciple, Huineng, saw it. Huineng had worked quietly in the kitchen for years, attracting little attention. Nevertheless he laughed at Shenxiu’s effort and put up a few lines of his own.

There is no mind
There is no mirror
This is the secret of secrets

 

The master Daman Hongren saw these two efforts.
That night he went discreetly to Huineng and gave him a bowl and a robe and, while acknowledging his enlightenment, asked him to leave the monastery, explaining that the other disciples would not accept him as Head Monk. After Huineng had gone Hongren awarded the prize, and the leadership of the monastery, to Shenxiu, his Chief Disciple.