瑜伽論記 5.175

5.175

三處難超越等者，此有二義：一云，所治有三，能治有三故名六法；一云，此取六對治，謂四無量則為四，無相等持為第五，我慢永盡為第六。

Regarding 'three places difficult to transcend, etc.', this has two meanings: one says that what is to be remedied has three, and what can remedy has three, hence they are called the six dharmas; the other says that this takes six antidotes, namely the four immeasurables constitute four, the signless concentration is the fifth, and the complete ending of the conceit "I am" is the sixth.