Shiva Purana
ज्ञानं प्रसन्नमेकाग्रमशेषोपाधिवर्जितम् ॥ योगाभ्यासेन युक्तस्य योगिनस्त्वेव सिध्यति ॥ २३ ॥
The clear and single-centred knowledge devoid of all conditioning factors can be achieved only by a Yogin who regularly practises Yoga.
english translation
jJAnaM prasannamekAgramazeSopAdhivarjitam ॥ yogAbhyAsena yuktasya yoginastveva sidhyati ॥ 23 ॥
hk transliteration by Sanscript