Yoking the coming and going of thought
tam yogam iti manyate sthiram indriya-dharanam apramattas tada bhavati yogo hi prabhavapyayau
Katha Upanishad 6.11
Yoga is considered to be the continuous concentration of the senses.
One then becomes attentive, thereby yoking the coming and going (of thought).
naiva vācā na manasā prāptum śakyō na cakṣuṣā
astīti bruvato’nyatra katham tadupalabhyatē
Katha Upanishad 6.12
Not by speech, nor by mind, nor by eye is it to be obtained.
How else can it be ascertained other than to ascertain for itself, “It is!”
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Trans. MWright