Chapter 6 · The Yoga of Meditation · Krishna said
Bhagavad Gita 6.25 — Stillness, step by step
शनैः शनैरुपरमेद् बुद्ध्या धृतिगृहीतया। आत्मसंस्थं मनः कृत्वा न किञ्चिदपि चिन्तयेत् ॥
śanaiḥ śanairuparamed buddhyā dhṛtigṛhītayā | ātmasaṃsthaṃ manaḥ kṛtvā na kiñcidapi cintayet ||
Meaning
— little by little, with an intellect held by patience, he should become still. Settling the mind in the Self, he should think of nothing else.