Philo Judaeus De Migratione Abrahami 34

[34] I am not ashamed to relate what has happened to me myself, which I know from having experienced it ten thousand times. Sometimes, when I have desired to come to my usual employment of writing on the doctrines of philosophy, though I have known accurately what it was proper to set down, I have found my mind barren and unproductive, and have been completely unsuccessful in my object, being indignant at my mind for the uncertainty and vanity of its then existing opinions, and filled with amazement at the power of the living God, by whom the womb of the soul is at times opened and at times closed up;