Rig Veda 3.62.10 (the Gayatri)

Klaus Klostermaier's survey of Hinduism describes a gap between how this verse functions inside its Vedic hymn and how it functions in the religion that grew from the Vedas, a gap already flagged on this passage: in the Rig Veda it is one verse addressed to Savitar, a solar deity, among many verses addressed to many gods, carrying no special liturgical mark of its own. Its transformation into the single most recited mantra in later Hinduism happened outside the Rig Veda's own text, through its adoption into the twilight worship, sandhyavandanam, performed at dawn and dusk by initiated members of the twice born castes.

That adoption came with a restriction the verse did not carry in its Vedic setting. Klostermaier describes the Gayatri as traditionally taught only at the upanayana, the sacred thread ceremony that marks a boy's ritual second birth into Vedic study, whispered privately by a teacher to the initiate rather than recited in open teaching the way this atlas's other passages generally circulate. That restricted transmission, alongside its constant private repetition afterward, is most of why a single verse from a hymn otherwise addressed mainly to specialists in Vedic recitation became, for the wider tradition, the mantra recited more than any other.