Bhagavad Gita · Jnana Karma Sannyasa YogaChapter 4, Shloka 18 (4.18)

Two readings (both scriptural, both important):

Shankaracharya — correcting a misperception. Karma = vyāpāra-mātram — mere activity. One who sees in activity akarma — karmābhāva — the absence of action (because the self is actionless; activity belongs to the body and senses), and who sees karma even in akarma — sitting still, doing nothing (because "I am doing nothing" is also agency tainted by ego; avidyā-bhūmau eva — all dealings of action and agent take place on the ground of ignorance) — that person is wise. Shankara gives a simile: nau-sthasya nāvi gacchantyāṃ taṭa-stheṣu agatiṣu nageṣu pratikūla-gati-darśanāt — to someone sitting in a moving boat, the motionless trees on the bank seem to move in the opposite direction; in the same way, through ignorance, action and inaction appear reversed — this verse corrects that viparyaya (inverted understanding).

Acharya Ramanuja — knowledge within action. Akarma-śabdena atra karmetarat prastutam ātma-jñānam ucyate — here "inaction" means knowledge of the self, which is distinct from action and is the subject at hand. Karmaṇi kriyamāṇe eva ātma-jñānaṃ yaḥ paśyet — one who sees knowledge of the self in the very performance of action, and akarmaṇi ca ātma-jñāne vartamāna eva yaḥ karma paśyet — who, abiding in knowledge of the self, sees action. That is, kriyamāṇam eva karma ātma-yāthātmyānusandhānena jñānākāraṃ yaḥ paśyet — the action being performed takes the form of knowledge through contemplation of the true nature of the self; and that knowledge, being within action, takes the form of action. Such a person is kṛtsna-śāstrārtha-vit — one who knows the meaning of the whole of scripture — and mokṣārhaḥ (fit for liberation).