This verse is from the Bhagavad Gita, Chapter 6, Verse 27. It is written in Sanskrit and translates to English as follows:
praśhānta-manasaṁ hyenaṁ yoginaṁ sukham uttamam
upaiti śhānta-rajasaṁ brahma-bhūtam akalmaṣham || 27 ||
“The Yogi whose mind is completely calm attains the highest happiness. His mind is freed from Rajoguna (restlessness and perversion). Such a Yogi becomes Brahmaswaroop (like Brahma) and is free from all doshas (sins)”
This verse describes the state of a yogi where he attains spiritual peace through meditation and sadhana. In this state, the yogi's mind is stable and calm, and he experiences inner happiness. The person becomes free from all disorders and fickleness and becomes like Brahma. Thus, through this verse, Sri Krishna emphasizes the importance of meditation and sadhana for yogis and explains how a person can attain spiritual peace and ultimate bliss through meditation.
Prashant - extremely calm
Manasam - the one with a calm mind (whose mind is calm)
Hi - certainly, indeed
Enam - this (to the Yogi)
Yoginaam - Yogi (person in meditation)
Sukham - bliss, happiness
Uttamam - the highest, the best
Upaiti - attains, to attain
Shanta - calm, peaceful
Rajasam - Rajoguna (restlessness and perversion of mind)
Brahmabhutam - Brahmaswaroop, like Brahma
Akalmasham - flawless, pure