The poem that you are possibly referring to is Shiva where Sri Aurobindo describes Shiva’s face as a mask of Peace.
‘Shiva
A face on the cold dire mountain peaks
    Grand and still; its lines white and austere
Match with the unmeasured snowy streaks
    Cutting heaven, implacable and sheer.
Above it a mountain of matted hair
    Aeon-coiled on that deathless and lone head
In its solitude huge of lifeless air
    Round, above illimitably spread.
A moon-ray on the forehead, blue and pale,
    Stretched afar its finger of chill light
Illumining emptiness. Stern and male
    Mask of peace indifferent in might!
But out from some Infinite born now came
    Over giant snows and the still face
A quiver and colour of crimson flame,
    Fire-point in immensities of space.
Light-spear-tips revealed the mighty shape,
    Tore the secret veil of the heart’s hold;
In that diamond heart the fires undrape,
    Living core, a brazier of gold.
This was the closed mute and burning source
    Whence were formed the worlds and their star-dance;
Life sprang, a self-rapt inconscient Force,
    Love, a blazing seed, from that flame-trance.’
Affectionately,
Alok Da
