4:18  

कर्मण्यकर्म यः पश्येदकर्मणि च कर्म यः ।
स बुद्धिमान्मनुष्येषु स युक्तः कृत्स्नकर्मकृत् ॥४-१८॥

karmaNyakarma yaH pashyedakarmaNi cha karma yaH ।

sa buddhimaanmanuShyeShu sa yuktaH kRRitsnakarmakRRit ॥४-१८॥

Source: Automatic ITRANS Transliteration

One who sees inaction in action, and one who sees action in inaction—
He is wise among humanity, he joined to perfect performance of actions.

Source: Milind S. Pandit

Attached action is selfish work that produces Karmic bondage, detached action is unselfish work or Seva that leads to nirvana, and forbidden action is harmful to society. The one who sees inaction in action, and action in inaction, is a wise person. Such a person is a yogi and has accomplished everything. (See also 3.05, 3.27, 5.08 and 13.29)

Source: The Bhagavad-Gita: The Sacred Song

One who sees inaction in action, and action in inaction, is intelligent among men, and he is in the transcendental position, although engaged in all sorts of activities.

Source: Bhagavad Gita As It Is