And with Him are the keys of the unseen; none knows them but He. And He knows whatsoever is in the land and in the sea. And there falls not a leaf but He knows it; nor is there a grain in the deep darkness of the earth, nor anything green or dry, but is recorded in a clear Book.
Islam, the Holy Qur’an, 6:60
Keys of the unseen knowledge are five which nobody knows but Allah: nobody knows what will happen tomorrow; nobody knows what is in the womb; nobody knows what he will gain tomorrow; nobody knows at what place he will die; and nobody knows when it will rain.
Islam, Saying of the Holy Prophet (sa), Sahih al-Bukhari, Hadith 1039
In comparison to witnessing something, belief in the unseen requires a kind of extra effort. Therefore, a muttaqi (or a righteous person) must, to a certain degree, make an intentional struggle. For when such a person attains the rank of a salih (or a virtuous servant), the unseen no longer remains hidden to such a person. A stream gushes forth from within such a one and reaches God. An individual of this nature witnesses God and His love with their eyes.
Islam, the Promised Messiah (as), Malfuzat – Vol. I, p. 27
For in him all things in heaven and on earth were created, things visible and invisible, whether thrones or dominions or rulers or powers – all things have been created through him and for him.
Christianity, The Bible, Colossians 1:16
There are many other large worlds, rolling through the immense space of vacuum, as the giddy goblins of Yakshas revel about in the dark and dismal deserts and forests, unseen by others.
Hinduism, Yoga Vasistha 3.30.34
Of the nether worlds and heavens has He created millions; Men exhaust themselves trying to explore them.
Sikhism, Adi Granth, Japuji 22, M.1, p. 5
O Omniscient Lord! Lifting up my hands in all humility to Thee, Who art Invisible and Munificent, I pray with joy for righteous actions, for benevolent thoughts, so that, I may thereby, let the soul of the universe rejoice.
Zoroastrianism, Yasna 28.1