The works of Ādi Śaṅkarācārya

Chāndogyopaniṣadbhāṣyam

Verse 44

चक्षुरेवर्गात्मा साम तदेतदेतस्यामृ-च्यध्यूढं साम तस्मादृच्यध्यूढं सामगीयते ।चक्षुरेव सात्मामस्तत्साम ॥ २ ॥

In plain words

The eye itself is the Ṛk, and the self is the Sāman. That Sāman rests upon this Ṛk. Therefore the Sāman is sung while resting upon the Ṛk. The eye is indeed the Ṛk, and the self is the Sāman; that is the Sāman. 2.

Close to the Sanskrit

The eye indeed is Ṛk, the self (reflection) is Sāman. That Sāman is mounted upon this Ṛk. Therefore Sāman is sung while mounted upon Ṛk. The eye indeed is that [Ṛk], the self is that [Sāman]; that is Sāman. 2.