Taittirīyopaniṣat 01.18

पृथिव्यन्तरिक्षं द्यौर्दिशोऽवान्तरदिशाः। अग्निर्वायुरादित्यश्चन्द्रमा नक्षत्राणि। आप ओषधयो वनस्पतय आकाश आत्मा। इत्यधिभूतम्। अथाध्यात्मम्। प्राणोव्यानोऽपान उदानः समानः। चक्षुः श्रोत्रं मनो वाक् त्वक्। चर्म मांसं स्नावाऽस्थिमज्जा। एतदधि विधाय ऋषिरवोचत्। पाङ्क्तं वा इदग्म् सर्वम्। पाङ्क्तेनैव पाङ्क्तं स्पृणोतीति ॥१८॥

Earth, atmosphere, sky, directions, and intermediate directions; fire, wind, sun, moon, and stars; waters, herbs, trees, space, and ego-principle — these are the elements. Now, pertaining to spiritual knowledge (adhyātmam): prāṇa, vyāna, apāna, udāna, and samāna; eye, ear, mind, speech, and skin; hide, flesh, sinews, bone, and marrow. Having arranged these, the sage declared: "All this is indeed fivefold. By the fivefold alone, the fivefold is completed."

Taittirīya Bhāshya 01.18

The word 'ātmā' in this context refers to the principle of ego. A reference is provided to a testimonial from Tattvasaṁhitā where Lord Hari, beginning with Nārāyaṇa empowers the six groups of five elements.

"पृथिव्याद्यं पाङ्क्तषट्कं पाङ्क्तेनैव स्वयं हरिः। नारायणादिरूपेण बलयत्यञ्जसा प्रभुः। इत्युवाच स्वयं विष्णुः वेदद्रष्टा गुणाधिकः॥"

"Lord Hari himself, in the form beginning with Lord Nārāyaṇa, empowers the six groups of five elements beginning with earth by the fivefold principle; thus spoke Lord Viṣṇu himself, the seer of the Veda and one endowed with supreme qualities."

इति तत्त्वसंहितायाम्॥

- stated thus in the Tattvasaṁhitā.

आत्मा अहङ्कारतत्त्वम्॥

The word 'ātmā' in this context refers to the principle of ego.