Bhagavad Gita 6.10
Let the student of spirituality try unceasingly to concentrate his mind; let him live in seclusion, absolutely alone, with his mind and personality controlled, free from desire and without possessions.
योगी युञ्जीत सततमात्मानं रहसि स्थितः।
एकाकी यतचित्तात्मा निराशीरपरिग्रहः॥yogī yuñjīta satatamātmānaṃ rahasi sthitaḥ|
ekākī yatacittātmā nirāśīraparigrahaḥ||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).