As Buddhist doctrine in general regards ignorance as the root of all sufferings and rejects the three poisons—greed, hatred, and delusion—and other unwholesome activities, Mazu’s unconditional identification of the complete, empirical human mind of good and evil, purity and defilement, enlightenment and ignorance with absolute Buddha-nature immediately provoked strong criticisms from more conservative quarters within the Chan movement. Nanyang Huizhong was the first to launch an attack. He criticized that “the south[ern doctrine] wrongly taught deluded mind as true mind, taking thief as son, and regarding mundane wisdom as Buddha wisdom.” Scholars in general agree that the target of this criticism was Mazu’s teaching. Huizhong himself advocated “this mind is the Buddha,” but he could not tolerate that Mazu included deluded mind in “this mind,” because he thought it betrayed and confused the basic teachings of Buddhism
Jia Jinhua, “Chan Doctrine and Practice of the Hongzhou School”, The Hongzhou School of Chan in Eighth- through Tenth-Century China, pg. 69