18:18  

ज्ञानं ज्ञेयं परिज्ञाता त्रिविधा कर्मचोदना ।
करणं कर्म कर्तेति त्रिविधः कर्मसंग्रहः ॥१८- १८॥

dnyaanaM dnyeyaM paridnyaataa triwidhaa karmachodanaa ।

karaNaM karma karteti triwidhaH karmasaMgrahaH ॥१८- १८॥

Source: Automatic ITRANS Transliteration

Knowledge, object of knowledge, knower: threefold impellers of action.
Instruments, action, agent: threefold constituents of action.

Source: Milind S. Pandit

The subject, the object, and the knowledge (of the object) are the threefold impetus to action. The (ten) organs, the Karma, and the Gunas are the threefold factors involved in any action.

Source: The Bhagavad-Gita: The Sacred Song

Knowledge, the object of knowledge and the knower are the three factors which motivate action; the senses, the work and the doer comprise the threefold basis of action.

Source: Bhagavad Gita As It Is