Bg 3.4

na karmaṇām anārambhān
naiṣkarmyaṁ puruṣo ’śnute
na ca sannyasanād eva
siddhiṁ samadhigacchati
Synonyms: 
na — not; karmaṇām — of prescribed duties; anārambhāt — by nonperformance; naiṣkarmyam — freedom from reaction; puruṣaḥ — a man; aśnute — achieves; na — nor; ca — also; sannyasanāt — by renunciation; eva — simply; siddhim — success; samadhigacchati — attains.
Translation: 
Not by merely abstaining from work can one achieve freedom from reaction, nor by renunciation alone can one attain perfection.
Purport: 

The renounced order of life can be accepted when one has been purified by the discharge of the prescribed form of duties which are laid down just to purify the hearts of materialistic men. Without purification, one cannot attain success by abruptly adopting the fourth order of life (sannyāsa). According to the empirical philosophers, simply by adopting sannyāsa, or retiring from fruitive activities, one at once becomes as good as Nārāyaṇa. But Lord Kṛṣṇa does not approve this principle. Without purification of heart, sannyāsa is simply a disturbance to the social order. On the other hand, if someone takes to the transcendental service of the Lord, even without discharging his prescribed duties, whatever he may be able to advance in the cause is accepted by the Lord (buddhi-yoga). Sv-alpam apy asya dharmasya trāyate mahato bhayāt. Even a slight performance of such a principle enables one to overcome great difficulties.