Bhagavad Gita 6.25 Chapter 6, Verse 25

शनैः शनैरुपरमेद् बुद्ध्या धृतिगृहीतया ।
आत्मसंस्थं मनः कृत्वा न किञ्चिदपि चिन्तयेत् ॥६.२५॥

śanaiḥ śanairuparamed buddhyā dhṛtigṛhītayā
ātmasaṃsthaṃ manaḥ kṛtvā na kiñcidapi cintayet

Meaning

one should gradually become still through an intellect held firm by patience; fixing the mind on the Self, one should think of nothing else.

Newly written by Bhajan Dhun — scholarly review in progress.

Reference: Bhagavad Gita 6.25 (Chapter 6, The Yoga of Meditation (Atma Samyama Yoga), Verse 25)