Actually, it is a spiritual concept of experiencing water/ENERGY everywhere, AND connecting to the formless and unknown BRAHMAN (i) first mentioned in the Rig Veda in an esoteric manner, then (ii) in Taittirīya-āraṇyaka as Prajapati lying on a lotus leaf and the dialogue between primordial tortoise and Prajapati and Prajapati experiencing the Universal form of the tortoise or BRAHMAN, and (iii) finally in Puranas as Sage Mārkaṇḍeya witnessing Vishnu/Krishna lying alone on a Banyan leaf.
(i) Rig Veda
Rig Veda 10.129.3 - says In the beginning (at the beginning of the meditation) there existed only darkness and the universe is filled with undistinguishable ENERGY. The unknown BRAHMAN was known through austerity.
सलिलं salilam indicates ENERGY, apart from water.
तम आसीत्तमसा गूळ्हमग्रेऽप्रकेतं सलिलं सर्वमा इदम् । तुच्छ्येनाभ्वपिहितं यदासीत्तपसस्तन्महिनाजायतैकम् ॥
tama āsīt tamasā gūḻham agre 'praketaṃ salilaṃ sarvam ā idam |
tucchyenābhv apihitaṃ yad āsīt tapasas tan mahinājāyataikam ||
English translation:
“There was darkness covered by darkness in the beginning, all this (world) was undistinguishable ENERGY (water); that empty united (world) which was covered by a mere nothing, was produced through the power of austerity.”
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Rig Veda 10.129.4 - says the rishis having meditated found the connection between existent with the non-existent - esoteric meaning - connection between the spiritual aspirant and the UNKNOWN BRAHMAN.
कामस्तदग्रे समवर्तताधि मनसो रेतः प्रथमं यदासीत् । सतो बन्धुमसति निरविन्दन्हृदि प्रतीष्या कवयो मनीषा ॥
kāmas tad agre sam avartatādhi manaso retaḥ prathamaṃ yad āsīt | sato bandhum
asati nir avindan hṛdi pratīṣyā kavayo manīṣā ||
English translation:
“In the beginning there was desire, which was the first seed of mind; sages having meditated in their hearts have discovered by their wisdom the connection of the existent with the non-existent.”
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(ii) Taittiriya Aranyaka
The first chapter of Taittiriya Aranyaka‟ contains an interesting mention of Prajapati lying on a Lotus leaf.
आपो॒ वा इ॒दमा॑सन्थ्सलि॒लमे॒व । स प्र॒जाप॑ति॒रेकः॑ पुष्करप॒र्णे सम॑भवत् ।
Indeed the universe is full of water and nothing else and Prajapati emerged on a lotus leaf.
अ॒न्त॒र॒तः कू॒र्मं भू॒तꣳ सर्प॑न्तम् । तम॑ब्रवीत् । मम॒ वैत्वङ्मा॒ꣳ॒सा । सम॑भूत् ॥ ०। १। २३। ९२॥
९३ नेत्य॑ब्रवीत् । पूर्व॑मे॒वाहमि॒हास॒मिति॑ । तत्पुरु॑षस्य पुरुष॒त्वम् । स
स॒हस्र॑शीर्षा॒ पुरु॑षः । स॒ह॒स्रा॒क्षस्स॒हस्र॑पात् । भू॒त्वोद॑तिष्ठत् ।
There after from the waters , kurma or tortoise crawled therein. Prajapati addressed the kurma: have you emerged from my „twang‟ or skin and „maamsa‟or flesh.
Kurma replied in the negative and said that even in the ancient times, that the concept of “Purushatwam‟ or virility of the universe accomplished its existence; the tortoise then assumed thousand heads and thousand eyes; the thousand eyes flashed from the waters.
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(iii) In Bhagavata Purana
Sage Mārkaṇḍeya witnesses a child/Vishnu lying on a Banyan leaf.
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So, the spiritual experience of an individual narrated esoterically in Rig Veda, was adopted and narrated as Prajapati lying on a Lotus leaf and having experience of primordial tortoise in Taittiriya Aranyaka and finally in Puranas as Sage Mārkaṇḍeya having the vision of primordial Vishnu.
