成唯識論演祕 6.139

6.139

彼有四說，第二說云：空是不動觸，無願是無所有觸，無相是無相觸，依三解脫以配三觸，餘繁不錄。

There are four explanations there; the second explanation says: Emptiness is immovable contact, wishlessness is nothingness contact, and signlessness is signless contact; they are matched with the three contacts based on the three liberations; the rest are numerous and not recorded.