Hi Prince,
Gayatri mantra is mentioned in Rig veda it is also known as savitri mantra. It is dedicated to Vedic Sun Deity. Gayatri Mantra is mentioned in the third Mandala (chapter) of Rig Veda. There are four Vedas The Rigveda, Sama veda, Yajurveda and Atharva veda. Vedas are large body of religious text.
Good luck
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