Rabbi Yehoshua and Trajan:
Babylonian Talmud, Tractate Hullin, 59b:
Another time the Emperor said to R. Yehoshua b. Hananiah, "I wish to see your God." He replied: ‘You are not able to see him." "Certainly," [said the Emperor], "I will see him." (60a) He went and positioned the Emperor facing the sun during the summer solstice and said to him, "Look at it’." He replied, "I cannot." R. Yehoshua said, "If at the sun which is but one of the ministers that attend the Holy One, blessed be He, you are unable to look, all the more so you are unable to look upon the divine presence!"