זוהר בראשית — דף קיב ע”א

The Zohar goes on to explain why Abraham said “she is my sister”: because of the Divine Presence, as it is written, “Say to wisdom, you are my sister.” “She is indeed my sister, the daughter of my father”: the daughter of the supreme Wisdom, but “not the daughter of my mother,” from the beginning of all that is hidden. Abraham called her his sister so that people would not go astray among the outer degrees and so that he would remain attached to faith, for a sister is not separated from her brother, whereas a wife may be. The people of the land were eager after the stars and constellations and served them. The text gives a sign: “and for his virgin sister.” Finally the verse “you shall fear the Lord your God” is cited: the particle et is the first degree, the place of fear, because it is judgment.