योगवासिष्ठः yogavāsiṣṭhaḥ - book-7, chapter-83, verse-30

निर्विकल्पसमाधिर्हि सिद्धान्तः सर्ववाड्मये ।
तच्च जीवदृषन्मौनं तूष्णीमेवात आस्यताम् ॥ ३० ॥

nirvikalpasamādhirhi siddhāntaḥ sarvavāḍmaye ,
tacca jīvadṛṣanmaunaṃ tūṣṇīmevāta āsyatām 30

30. It is the unalterable steadiness of the mind, which is the ultimate samadhi or perfection of all sastras; therefore the living yogi aught to remain, as the mute and immovable stone in his meditation.