what is biggest entity in hinduism, I thought its Brahman, If it is, then please write, mantra, stotra, or any verses related to Brahman
Brahman is an ABSTRACT thing.
The Veda, Upanishads, etc, described Brahman in many ways. Lengthy discourses were recorded on this subject.
Mahavakyas will describe in a nutshell about Brahman.
The Mahavakyas (sing.: mahāvākyam, महावाक्यम्; plural: mahāvākyāni, महावाक्यानि) are "The Great Sayings" of the Upanishads, as characterized by the Advaita school of Vedanta.
Most commonly, Mahavakyas are considered four in number.
Prajnanam Brahma (प्रज्ञानम् ब्रह्म) Ayam Atma Brahma (अयम् आत्मा ब्रह्म) Tat Tvam Asi (तत् त्वम् असि) Aham Brahma Asmi (अहम् ब्रह्मास्मि)