This is one of the poems in the Cantong qi (The Seal of the Unity of the Three), the main text of Taoist Internal Alchemy (Neidan).
Innerly nourish yourself,
serene and quiescent in Empty Non-Being.
Going back to the fundament conceal your light,
and innerly illuminate your body.
"Shut the openings"
and raise and strengthen the Numinous Trunk;
as the three luminaries sink into the ground,
warmly nourish the Pearl.
"Watching, you do not see it" —
it is nearby and easy to seek.
For comments and notes on this poem, see this page
Reproduced form Fabrizio Pregadio, The Seal of the Unity of the Three: A Study and Translation of the Cantong qi, the Source of the Way of the Golden Elixir (© Golden Elixir Press, forthcoming).