MĀṆḌŪKYA UPANISHAD · 10

स्वप्नस्थानस्तैजस उकारो द्वितीया मात्रोत्कर्षात्
उभयत्वाद्वोत्कर्षति ह वै ज्ञानसन्ततिं समानश्च भवति
नास्याब्रह्मवित्कुले भवति य एवं वेद ॥ १०॥

svapnasthānastaijasa ukāro dvitīyā mātrotkarṣāt
ubhayatvādvotkarṣati ha vai jñānasantatiṃ samānaśca bhavati
nāsyābrahmavitkule bhavati ya evaṃ veda ॥ 10॥

The Dreamer, Taijasa, the Inhabitant in Luminous Mind, He is U, the second letter, because of Advance and Centrality; he that knoweth Him for such, advanceth the bounds of his knowledge and riseth above difference; nor of his seed is any born that knoweth not the Eternal.

Sri Aurobindo · CWSA 18, p. 195