KAṬHA UPANISHAD · 1.2.12

तं दुर्दर्शं गूढमनुप्रविष्टं
गुहाहितं गह्वरेष्ठं पुराणम् ।
अध्यात्मयोगाधिगमेन देवं
मत्वा धीरो हर्षशोकौ जहाति ॥ १२॥

taṃ durdarśaṃ gūḍhamanupraviṣṭaṃ
guhāhitaṃ gahvareṣṭhaṃ purāṇam ।
adhyātmayogādhigamena devaṃ
matvā dhīro harṣaśokau jahāti ॥ 12॥

Realising God by attainment to Him through spiritual Yoga, even the Ancient of Days who hath entered deep into that which is hidden and is hard to see, for he is established in our secret being and lodged in the cavern heart of things, the wise and steadfast man casts far from him joy and sorrow.

Sri Aurobindo · CWSA 18, p. 110