One of his (Siva's) eyes is like the sun, another is like the moon, and his third eye, which is between his eyebrows, is like fire. He can generate fire from his middle eye, and he is able to vanquish any powerful living entity, including Brahma
SB Canto 3
Lord Śiva's body is reddish, and he is unstained, but he is covered with ashes. His hair is dusty from the whirlwind dust of the burning crematorium. He is the younger brother of your husband, and he sees with his three eyes.
Lord Śiva is not an ordinary living entity, nor is he in the category of Viṣṇu, or the Supreme Personality of Godhead. He is far more powerful than any living entity up to the standard of Brahmā, yet he is not on an equal level with Viṣṇu. Since he is almost like Lord Viṣṇu, Śiva can see past, present and future. One of his eyes is like the sun, another is like the moon, and his third eye, which is between his eyebrows, is like fire. He can generate fire from his middle eye, and he is able to vanquish any powerful living entity, including Brahmā, yet he does not live pompously in a nice house, etc., nor does he possess any material properties, although he is master of the material world. He lives mostly in the crematorium, where dead bodies are burnt, and the whirlwind dust of the crematorium is his bodily dress. He is unstained by material contamination. Kaśyapa took him as his younger brother because the youngest sister of Diti (Kaśyapa's wife) was married to Lord Śiva. The husband of one's sister is considered one's brother. By that social relationship, Lord Śiva happened to be the younger brother of Kaśyapa. Kaśyapa warned his wife that because Lord Śiva would see their sex indulgence, the time was not appropriate. Diti might argue that they would enjoy sex life in a private place, but Kaśyapa reminded her that Lord Śiva has three eyes, called the sun, moon and fire, and one cannot escape his vigilance any more than one can escape Viṣṇu. Although seen by the police, a criminal is sometimes not immediately punished; the police wait for the proper time to apprehend him. The forbidden time for sexual intercourse would be noted by Lord Śiva, and Diti would meet with proper punishment by giving birth to a child of ghostly character or a godless impersonalist. Kaśyapa foresaw this, and thus he warned his wife Diti.