Sefer Yetzirah
Chapter III
The three mother letters A, M, SH are the foundations of the whole; and resemble a Balance, the good in one scale, the evil in the other, and the oscillating tongue of the Balance between them.
These three mothers enclose a mighty mystery, most occult and most marvelous, sealed as with six rings, and from them proceed primeval Fire, Water, and Air; these are subsequently differentiated into male and female. At first existed these three mothers, and there arose three masculine powers, and hence all things have originated.
The three mothers are A, M, SH; and in the beginning as to the Macrocosm the Heavens were created from Fire;nthe Earth from primeval Water; and the Air was formed from the Spirit, which stands alone in the midst, and is the Mediator between them.
In the Year or as regards Time, these three mothers represent Heat, Cold, and a Temperate climate, the heat from the fire, the cold from the water, and the temperate state from the spiritual air which again is an equalizer between them.