Bhagavad Gita 6.25
शनैः शनैरुपरमेद्बुद्ध्या धृतिगृहीतया। आत्मसंस्थं मनः कृत्वा न किञ्चिदपि चिन्तयेत्।।6.25।।
śanaiḥ śanairuparamedbuddhyā dhṛtigṛhītayā| ātmasaṃsthaṃ manaḥ kṛtvā na kiñcidapi cintayet||6.25||
shanaih shanairuparamedbuddhya dhritigrihitaya atmasamstham manah kritva na kincidapi cintayet6.25
Meaning
Gradually, step by step, with full conviction, the intellect should be settled in the Self. Making the mind established in the Self, one should think of nothing else.
शनैः शनैः धैर्ययुक्त बुद्धि के द्वारा (योगी) उपरामता (शांति) को प्राप्त होवे; मन को आत्मा में स्थित करके फिर अन्य कुछ भी चिन्तन न करे।
This is verse 25 of 47 in Chapter 6 (Dhyana Yoga) of the Bhagavad Gita.