Muṇḍaka Upaniṣad 2.2.3.p1

2.2.3.p1

yasyāgnihotriṇo'gnihotramadarśaṃ darśākhyena karmaṇā varjitam| agnihotriṇo'vaśyakartavyatvād darśasya| agnihotrasambandhyagnihotraviśeṣaṇamiva bhavati| tadakriyamāṇamityetat| tathā paurṇamāsam ityādiṣvapyagnihotraviśeṇatvaṃ draṣṭavyam, agnihotrāṅgatvasya aviśiṣṭatvāt| apaurṇamāsaṃ paurṇamāsakarmavarjitam, acāturmāsyaṃ cāturmāsyakarmavarjitam, anāgrayaṇamāgrayaṇaṃ śaradādikartavyaṃ tacca

3. Having taken the how furnished by the Upanishads, the great weapon—and fixed in it the arrow rendered pointed by constant meditation and having drawn it with the mind fixed on the Brahman, hit, good looking youth! at that mark—the immortal Brahman.