Śaiśirīya Śikṣā 6

6

prākṛte saṃskṛte vāpi svayaṃ proktāḥ svayaṃbhuvā
svarā viṃśatirekaśca sparśānāṃ pañcaviṃśatiḥ

in Prakrit or in Sanskrit, uttered by the Self-born Himself: / twenty-one vowels, twenty-five stop consonants,