Kena Upanishad 1:6-7-8 (fifth time is the charm)

Which by the eye is not seen but by which the seeing is seen,

That alone, the Absolute, You, know, and not this which they worship.

yac cakshusha na pashyate yena cakshumshi pashyati

tad eva brahma tvam viddhi nedam yad idam upaasate

Which by the ear is not heard but by which the hearing is heard,

That alone, the Absolute, You, know, and not this which they worship.

yac chrotrena na shrinoti yena shrotram idam shrutam

tad eva brahma tvam viddhi nedam yad idam upaasate

Which by the breath is not inhaled but by which the breathing is exhaled,

That alone, the Absolute, You, know, and not this which they worship.

yat pranena na praniti yena pranah praniyate

tad eva brahma tvam viddhi nedam yad idam upaasate

Note: There's not much to say about these, except they continue the Absolute mantra from the previous two slokas (I've decided, for the time being, that 'you' should be capitalized), as well as the concept that the senses cannot detect it but it detects the senses: awareness. I feel the last sloka involving the breath is particularly wonderful in denoting the breath of life not inhaling (smelling) That, but the breath of life being exhaled by That. Nice ending there.