Transliteration
anāśritaḥ karma-phalaṃ kāryaṃ karma karoti yaḥ |
sa saṃnyāsī ca yogī ca na nir-agnir-na cākriyaḥ || 1 ||
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Translation
The Blessed Lord said: One who performs obligatory works without expecting their fruits — is a Sanyāsin and Yogi, and not one who does not maintain sacred fires and performs no (prescribed) actions.
Purport
In this Shloka Bhagvan Shri Krishna gives the definition of Sanyas. Bhagvan says, in reality, renouncing the karma and worldly duty is not sanyas. Sanayas lies in renouncing the fruits of actions and not action. A human who performs his human duty with sincerity without having selfish desires from the actions in real is a Sanyasi. And since he engages in Karma is yogi too. So anybody who performs Karma yoga properly is Sanyasi too.
Rather one who runs away from their duties leaves karma is against the principle of Sanyas. This Shloka hence describes the real definition of Sanayas and also establishes that in principle Karma Yoga and Sanyas trace the same path. A yogi is automatically a Sanyasi too.