Creation and Destruction - Mundaka Upanishad Chapter2, Canto1 Verse1
तदेतत्सत्यं यथा सुदीप्तात्पावकाद्विस्फुलिङ्गाः सहस्रशः प्रभवन्ते सरूपाः ।
तथाक्षराद्विविधाः सोम्य भावाः प्रजायन्ते तत्र चैवापि यन्ति ॥ १ ॥
yathaa sudiptaappaabakaad bisphulingaah sahasrashah prabhabante saroopaah
tathaa akhyaraad bibidhaah somya bhaabaah prajaayante tatra chaiwaapi yanti
(Mundaka Upanishad Chapter2, Canto1 Verse1)
“That is Truth”
Like, from a blazing fire, thousands of bright sparks fly out in different directions which have the same power and properties of the main blazing fire, similarly, O’ my divine disciple, from the imperishable, come out and merge into It again, innumerable different species of beings.
In this verse, the Saint Teacher (Rishi) is personally teaching the spiritually fit disciple about God, the supreme soul and the Innumerable creatures who get created from Him.
During Pralaya or the Great Delusion (Final Cosmic withdrawal) all these beings are absorbed (merged back) into the Supreme Soul