Om Bhur Bhuvah Svah Tat Savitur Varenyam Bhargo Devasya Dhimahi Dhiyo Yo Nah Prachodayat
The Gayatri Mantra, found in the Rig Veda, is considered the most sacred of all Vedic mantras. Addressed to Savitar (the sun deity representing divine illumination), it is a prayer for spiritual enlightenment and the awakening of intelligence.
Translation: "We meditate on the glory of the Creator who has created the universe, who is worthy of worship, who is the embodiment of knowledge and light, who is the remover of all sin and ignorance. May He enlighten our intellect."
The mantra consists of three parts: invocation of the three realms (earth, atmosphere, heaven), meditation on the divine source of light, and a prayer for awakening higher consciousness. Its 24 syllables are said to represent the 24 principles of creation.
Traditionally chanted at dawn, noon, and dusk, the Gayatri Mantra is practiced across Hindu traditions. Its recitation is believed to purify the mind, awaken spiritual insight, and connect the practitioner with universal consciousness.
Source
Rig Veda 3.62.10