This verse is from the Bhagavad Gita, Chapter 6, Verse 37. It is written in Sanskrit and translates to English as follows:
arjuna uvācha
ayatiḥ śhraddhayopeto yogāch chalita-mānasaḥ
aprāpya yoga-sansiddhiṁ kāṅ gatiṁ kṛiṣhṇa gachchhati || 37 ||
"A person who is not fully steadfast in his practice. One who has started practising Yoga with devotion and faith. A person whose mind has turned away from the practice of Yoga. Without attaining the full perfection of Yoga. What will be his result. O Krishna, what state does he go to."
Explanation in detail:
This question of Arjuna reveals the anxiety of those practitioners who start spiritual practice with faith and devotion but for some reason are not able to remain steadfast in their practice.
Ayaati: - one who is striving
Shraddhaya - faith
Upeta: - engaged
Yogaat - yoga
Chalitmanas: - one with a distracted mind
Apraapya Yogasamsiddhim: - without attaining the full perfection of yoga.
Kaan Gati: - what state
Krishna: - O Krishna.
Gacchati: - goes