Zohar 3:49b

Jewish Mysticism
The sexual intercourse of [the Jewish] male is restricted to designated times so that he may direct his will to be conjoined to the Holy One, blessed be he. Thus they have taught- At midnight the Holy One, blessed be he, enters the Garden of Eden to take delight with the righteous, and the Community of Israel praises the Holy One, blessed be he, and this is the acceptable time to be conjoined to them. The comrades who are engaged in [study of] Torah join the Community of Israel in praising the holy King as they are occupied with the Torah. For the rest of the [Jewish] males this is the acceptable time to be sanctified in the sanctity of the Holy One, blessed be he, and to direct their intention to be conjoined to him. With respect to the comrades who are engaged in [study of] Torah, the time for their sexual intercourse is the time that another intercourse takes place, and this is on the eve of Sabbath.

Translated by Elliot Wolfson in “Eunuchs who Keep the Sabbath- Becoming Male and the Ascetic Ideal in Thirteenth Century Jewish Mysticism,” in Becoming Male in the Middle Ages, 151-185. Edited by J. J. Cohen and B. Wheeler. New York- Garland, 1997.