पुरा प्रातरनुवाकस्योपाकरणाज्जघनेन गार्हपत्यस्योदाङ्मुख उपविश्य स वासवं सामाभिगायति ॥ २.२४.३ ॥
In plain words
Before the beginning of the morning litany, let him sit down behind the householder's fire facing north and sing the Sāman of the Vasus:
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
किं तद्वेद्यमिति, आह— पुरा पूर्व प्रातरनुवाकस्य श स्त्रस्य प्रारम्भात् जघनेन गार्हपत्यस्य पश्चात् उदङ्मुख सन् उपविश्य स वासव वसुदैवत्य साम अभिगायति ॥
In plain words
What is that which is to be known? The text explains: before the morning recitation and praise begin, sitting behind the householder's fire facing north, he sings the vāsava sāman dedicated to the Vasus.
Close to the Sanskrit
What is that to be known? It replies: prior to the start of the morning recitation and śastra, sitting behind the householder's fire facing north, he sings the vāsava sāman dedicated to the Vasus.