Chandogya Upanishad
Prapathaka VIII, Khanda 4
That Self is a bank , a boundary, so that these worlds may not be confounded. Day and night do not pass that bank, nor old age, death, and grief; neither good nor evil deeds. All evil-doers turn back from it, for the world of Brahman is free from all evil.
Therefore he who has crossed that bank, if blind, ceases to be blind; if wounded, ceases to be wounded; if afflicted, ceases to be afflicted. Therefore when that bank has been crossed, night becomes day indeed, for the world of Brahman is lighted up once for all .