Bhagavatapurana 2.6.40

2.6.40

ṛṣe vidanti munayaḥ praśāntātmendriyāśayāḥ /
yadā tadevāsattarkaistirodhīyeta viplutam //

40. O sage (Narada)! Sages do realise Him, when they attain purity of body, serenity of mind and control of the senses; but the same Truth disappears from their view, when it is assailed by the reasonings of the unrighteous (i.e., unbelievers or miscreants).