Bhagavad Gita Chapter 18, Verse 7

नियतस्य तु सन्न्यासः कर्मणो नोपपद्यते | मोहात्तस्य परित्यागस्तामसः परिकीर्तितः ||

niyatasya tu sannyāsaḥ karmaṇo nopapadyate mohāt tasya parityāgas tāmasaḥ parikīrtitaḥ

Renunciation of prescribed duties is not proper. Abandonment of duty out of delusion is declared to be tamasic.

Krishna explains the first kind of improper relinquishment. 'Niyatasya tu sannyāsaḥ karmaṇo nopapadyate'—renunciation of prescribed duties (niyatasya karmaṇaḥ) is not proper (na upapadyate). Prescribed duties (yajña, dāna, tapaḥ) should not be renounced. Then he explains what happens when someone does abandon them: 'mohāt tasya parityāgaḥ tāmasaḥ parikīrtitaḥ'—abandonment (parityāgaḥ) of duty out of delusion (mohāt) is declared to be tamasic (tāmasaḥ). This is the first kind of improper tyaga: abandoning prescribed duties out of ignorance or delusion. It's tamasic because it comes from misunderstanding—thinking you should renounce duty when you should perform it with detachment. This clarifies the distinction: you don't renounce prescribed duties, you perform them without attachment.