成唯識論述記 6.112

6.112

述曰：此經部師以經三學中，說為心學；靜慮支中，說為心一境性，故離心無。

The Commentary states: This master of the Sautrāntika school [reasons that] because among the three trainings in the sūtra, it is spoken of as the training in mind (cittasikṣā), and among the limbs of dhyāna, it is spoken of as one-pointedness of mind (cittaikāgratā), therefore it does not exist apart from mind.