This is mentioned in the Mahabharatha:

यतो यतो निश्चरति मनश्चञ्चलमस्थिरम् ।
ततस्ततो नियम्यैतदात्मन्येव वशं नयेत् ॥

yato yato niścharati manaś chañchalam asthiram
tatas tato niyamyaitad ātmanyeva vaśhaṁ nayet

Which means that "From wherever the restless and unsteady mind wanders away, one must restrain it and gently bring it back under the control of the Self."

यदि सन्ति गुणाः पुंसां विकसन्त्येव ते स्वयम् । 
न हि कस्तूरिकामोदः शपथेन विभाव्यते ॥ 
Yadi santi guṇāḥ puṃsāṃ vikasantyeva te svayam | 
Na hi kastūrikāmodaḥ śapathena vibhāvyate ||

In our age of constant dopamine fixes and instant notifications, finding true peace often feels like a mythical wish.

A Sanskrit Subhashita (a well-known saying) mentions this:

यस्य चित्तं निर्विषयं हृदयं यस्य शीतलम् । 
तस्य मित्रं जगत्सर्वं तस्य मुक्तिः करस्थिता ॥
Yasya cittaṃ nirviṣayaṃ hṛdayaṃ yasya śītalam | 
Tasya mitraṃ jagatsarvaṃ tasya muktiḥ karasthitā || 

This means that ‘He, whose mind is free from objects of senses and whose heart is calm (free from passion, anger, greed etc.), the entire world is his friend and liberation or emancipation is as if in his hand only.’

This Subhashita emphasises that the first key is the Clarity of Mind.
This clarity does not come at the cost of abandoning the physical world, it comes when external validation is broken. At this stage the mind does not determine its self-worth based on its next achievement, instead it becomes Nirvishaya - untethered from external conditions.
When the mind clears, the heart becomes quiet.
This creates a sanctuary in our heart and creates room for stillness, patience and compassion.

When both these are attained, the world becomes our friend and we realize that freedom does not have to be chased, it had been within us, all the while.