I propose the statement is vindicated even without a direct reference, since we have solid references dating the RV to 1500-1000 BC over at Rigveda; the Gayatri mantra is Rigvedic, and the Vedic chant traditions include the Gayatri mantra; thus it stands to reason that at least part of the tradition is aged more than 3,000 years, plus we have no candidate that can hope to tie with this.