MUṆḌAKA UPANISHAD · 1.2.1

तदेतत्सत्यं मन्त्रेषु कर्माणि कवयो
यान्यपश्यंस्तानि त्रेतायां बहुधा संततानि ।
तान्याचरथ नियतं सत्यकामा एष वः
पन्थाः सुकृतस्य लोके ॥ १॥

tadetatsatyaṃ mantreṣu karmāṇi kavayo
yānyapaśyaṃstāni tretāyāṃ bahudhā saṃtatāni ।
tānyācaratha niyataṃ satyakāmā eṣa vaḥ
panthāḥ sukṛtasya loke ॥ 1॥

This is That, the Truth of things: works which the sages beheld in the Mantras were in the Treta manifoldly extended. Works do ye perform religiously with one passion for the Truth; this is your road to the heaven of good deeds.

Sri Aurobindo · CWSA 18, p. 133