The works of Ādi Śaṅkarācārya

Chāndogyopaniṣadbhāṣyam

Verse 112

पुरा प्रातरनुवाकस्योपाकरणाज्जघनेनगार्हपत्यस्योदङ्मुख उपविश्य स वासव५सामाभिगायति ॥ ३ ॥

In plain words

Before the morning recitation begins, sitting behind the householder's fire facing north, he sings the vāsava sāman.

Close to the Sanskrit

Before the commencement of the morning recitation, seated behind the householder's fire facing north, he chants the vāsava sāman.