Right here

(And, well, elf wasn't a class of its own in "earlier editions". In the original three-booklet set, an elf was automatically a character who could switch between Fighting Man and Magic-User, which were both standard classes. When the Thief class was introduced in old D&D, elves could be thieves. Then, in AD&D, elf was a race of its own. Only in the offshoot D&D branch, starting with the Holmes boxed set and designed specifically as an introductory version was elf made a class — and Gary Gygax wasn't the author of those versions.)

Wasn't it "half-elves" that were the hybrid mage/warrior? Ah, my misspent college days locked in the Whig-Clio basement at Princeton.

No, it was elves. My first character, circa 1979, was such.