Bhagavan Shri Krishna said: One who performs his prescribed duties and renounces the results of those actions is a yogi and a sannyasi. One does not become a sannyasi simply by rejecting the performance of sacrifice and performing no activities.
Bhagavad Gita - Chapter 6 - Dhyana Yoga - The Yoga of Meditation
O son of Pandu, that which is known as sannyasa is the same as yoga. One can never become a yogi without renouncing the desire to satisfy the senses.
For one who is a beginner on the path of yoga, action is the means. For one who is already practiced in yoga, the renunciation of action is the means.
When one is neither attached to the sense-objects nor to the activities that lead to their enjoyment, at that time one is said to have attained yoga.
Living beings must elevate themselves by the mind – they must not degrade themselves. Certainly, the mind is the friend of the living beings as well as their worst enemy.
For one who has subdued the mind, the mind is a friend. However, for one who has not controlled the mind, the mind is the greatest enemy.
Those who have subdued the mind and are calm, attain realization of Paramatma (Super Consciousness). For such persons heat and cold, happiness and distress and honor and dishonor are all the same.
The yogi who is self-satisfied due to his knowledge and realization, fixed in his spiritual nature and in control of his senses, sees dirt, stones and gold equally.
Such a yogi of impartial intelligence sees an honest wellwisher, an affectionate benefactor, an enemy, neutral persons, a mediator, the envious, a relative, the pious and the impious with equal vision.
A yogi should live in a solitary place with his mind and body fully controlled. He should be without desire, without a sense of possessiveness and must constantly fix his mind on the atma, the self within.