Taittirīyopaniṣat 01.13

भूर्भुवस्सुवरिति वा एतास्तिस्रो व्याहृतयः तासा मु ह स्मैतां चतुर्थीम्। माहाचमस्यः प्रवेदयते। मह इति। तद् ब्रह्म। स आत्मा। अङ्गान्यन्या देवताः ॥१३॥

The words 'bhūḥ', 'bhuvaḥ', and 'suvaḥ' are the three sacred utterances; indeed, the great sage Chamasa teaches the fourth, 'maha'. That is Brahman. He is the Ātmān. The other deities are his limbs.

Taittirīya Bhāshya 01.13

Lord Hari, who is the Lord of the Vedas, is clearly manifest from the immortal sounds of the Vedas. He is called 'Brahmakosha' i.e. the repository of Brahman, as he is the abode of the Vedas; is called 'Bhaga' as he is full of the six qualities; and is called 'Vibhu' as he possesses manifold forms. The four Vyahritis 'Bhū', 'Bhuvaḥ', 'Suva' and 'Maha' correspond to the Aniruddha, Pradyumna, Sankarshana, and Vāsudeva forms of the Lord, respectively. Each of them corresponds to the head, arms, feet, and the centre (heart).

"यो विश्वरूपो भगवान् छन्दसामधिपो हरिः। छन्दोभ्योऽमृतरूपेभ्यः सुव्यक्तस्तदुपासनात् ॥ मेधावी तत्त्वविज्ञानी भूत्वा क्षिप्रं विमुच्यते॥"

"He who is Hari, the Lord of the Vedas and of universal form, is clearly manifest from the immortal forms of the Vedas through worship. Such an intelligent one, having become the knower of the truth, is quickly liberated."

इति च।

- stated thus as well.

"वेदावासत्वतो विष्णुः ब्रह्मकोश इति स्मृतः। भगः षड्गुणपूर्णत्वात् बहुरूपत्वतो विभुः॥ सहस्रशाख इत्युक्तस्तमुपास्य जनार्दनम्। मुच्यते नात्र सन्देहः सर्वभोगैश्च युज्यते॥"

Viṣṇu is called 'Brahmakosha' i.e. the repository of Brahman, because he is the abode of the Vedas (knowledge); 'Bhaga', being full of the six qualities; and 'Vibhu', as he possesses manifold forms. It is said that whoever worships Janardana, who is described as 'Sahasraśākha' i.e. thousand-branched, is surely liberated and enjoys all pleasures; there is no doubt about this.

इति प्रक्लृप्ते।

- stated thus in the ancient text called 'Praklṛpte'.

"आवहन्ती चिरं सर्वभोगान् या श्रीस्सनातनी। तां मय्यावह गोविन्द सुशिखण्डोपशोभिताम्॥"

"O Govinda, bring unto me that eternal Śrī (prosperity), adorned with beautiful crest-feathers, who brings all enjoyments for a long time."

इति च ॥१२॥

- stated thus.

भूरादि व्याहृतीभिस्तु वाच्यं मूर्तिचतुष्टयम्। अनिरुद्धादिकं वासुदेवान्तं देहमध्यगः॥

The fourfold form, starting from Bhū and the other Vyāhṛtis, should be described; these forms correspond from Aniruddha to Vāsudeva (Aniruddha, Pradyumna, Sankarshana, and Vāsudeva), and are situated in the middle of the body.

वासुदेवो महोनामा त्वनिरुद्धश्शिरो मतः। भूर्नामाथ भुवोनामा बाहू प्रद्युम्न ईरितः॥

Vāsudeva is called 'Maha', the great one , but Aniruddha is regarded as the head, denoted by the sound 'Bhūḥ'. The arms are said to be Pradyumna, denoted by the sound 'Bhuvaḥ'.

सङ्कर्षणस्सुवर्नामा पादौ तस्य महात्मनः। अनन्योऽप्यन्यशब्देन चतुरात्मा प्रकीर्त्यते॥

Saṅkarṣaṇa is regarded as the feet, denoted by the sound 'Suva'; that essence is also called 'Maha'; as he is also donated by the word 'Anya' i.e. 'another'; and is proclaimed to have four forms.

निर्विशेषोऽपि भगवान् सङ्ख्यामात्रविशेषतः ॥१३॥

Even though the Lord is without distinction, He is considered distinct only by the difference in number.