Hinduism
It is generally asserted that Hindu religious texts are the oldest known literature that contains Pantheistic ideas. In Hindu theology, Brahman is the unchanging, infinite, immanent, and transcendent reality which is the Divine Ground of all things in this Universe, and is also the sum total of all that ever is, was, or ever shall be. "poornamadah poornamidam" which in Sanskrit means "That is whole, this is whole." This idea of pantheism is traceable from some of the more ancient Vedas and Upanishads to later Advaita philosophy. All Mahāvākyas (Great Sayings) of the Upanishads, in one way or another, seem to indicate the unity of the world with the Brahman. Chāndogya Upanishad says "All this Universe indeed is Brahman; from him does it proceed; into him it is dissolved; in him it breathes, so let every one adore him calmly". It further says "This whole universe is Brahman, from Brahman to a clod of earth. Brahman is both the efficient and the material cause of the world. He is the potter by whom the vase is formed; He is the clay from which it is fabricated. Everything proceeds from Him, without waste or diminution of the source, as light radiates from sun. Everything merges into Him again, as bubbles bursting mingle with air – as rivers fall into the ocean. Everything proceeds from and returns to Him, as the web of the spider is emitted from and retracted into itself." In the hymns of the Rig-veda, a pantheistic strain of thought may be discernible in the tenth book (10-121).
This concept of God is of one unity, with the individual personal gods being aspects of the One; thus, different deities are seen by different adherents as particularly well suited to their worship. As the sun has rays of light which emanate from the same source, the same holds true for the multifaceted aspects of God emanating from Brahman, like many colors of the same prism. Also Hindus worship Nature by offering prayers to sacred trees, groves and also to animals. It's believed widely among Hindus that God lives in all, a very pantheistic belief. Vedanta, specifically, Advaita, is a branch of Hindu philosophy which gives this matter a greater focus. Most Vedantic adherents are monists or "non-dualists" (i.e. Advaita Vedanta), seeing multiple manifestations of the one God or source of being, a view which is often considered by non-Hindus as being polytheistic.