大般涅槃經義記 9.54

9.54

自下第七約三三昧以別三門。說空三昧以之為「定」，住第一義心不動故。無願名「慧」，慧見生死生厭離故。無相名「捨」，捨眾相故。

From here below, the seventh part distinguishes the three approaches in terms of the three samādhis. Speaking of emptiness samādhi as "concentration," it is because abiding in the ultimate truth, the mind is unmoving. Signlessness is named "wisdom," because wisdom sees saṃsāra and gives rise to revulsion. Wishlessness is named "equanimity," because it relinquishes all marks.