Bg 18.24

yat tu kāmepsunā karma
sāhaṅkāreṇa vā punaḥ
kriyate bahulāyāsaṁ
tad rājasam udāhṛtam
Word for word: 
yat — that which; tu — but; kāma-īpsunā — by one with desires for fruitive results; karma — work; sa-ahaṅkāreṇa — with ego; vā — or; punaḥ — again; kriyate — is performed; bahula-āyāsam — with great labor; tat — that; rājasam — in the mode of passion; udāhṛtam — is said to be.
Translation: 
But action performed with great effort by one seeking to gratify his desires, and enacted from a sense of false ego, is called action in the mode of passion.