俱舍論記 26.58

26.58

「不定心者至能治彼故」者，第九對不定、定心。謂能治彼散動之心，即是定心。故《婆沙》云「不定心者，謂染污心，散亂相應故。定心者，謂善心，等持相應故。」

Regarding "The unconcentrated mind ... because it can counteract that": this is the ninth pair, unconcentrated mind (asamāhita-citta) and concentrated mind (samāhita-citta). That which can counteract that distracted mind is the concentrated mind. Thus the Mahāvibhāṣā says: "The unconcentrated mind refers to the defiled mind, because it is associated with distraction (vikṣepa). The concentrated mind refers to the wholesome mind, because it is associated with meditative absorption (samādhi)."