Markandeyapurana 42.5

42.5

nirguṇā yogigamyānyā cārdhamātrordhvasaṃsthitā /
gāndhārīti ca vijñeyā gāndhārasvarasaṃśrayā //

A and U and M are its three letters; these are its three instants; they are characterized by goodness, passion and ignorance. And another, a half instant,[1] which has its seat on the top of the syllable, is without quality and can be understood by yogis only. It is called gāndhārī,[2] as it is to be uttered in the gāndhāra note.[3] Being pronounced it reaches the head, and it conveys the feeling of ants moving over the body.