Muṇḍaka Upaniṣad 2.2.4

2.2.4

praṇavo dhanuḥ śaro hy ātmā brahma tal lakṣyam ucyate.
apramattena veddhavyaṃ śaravat tanmayo bhavet.

4. The mystic syllable Om (praṇava) is the bow. The arrow is the soul (ātman).
Brahma is said to be the mark (lakṣya).
By the undistracted man is It to be penetrated.
One should come to be in It, as the arrow [in the mark].