Sefer HaHinnukh 209
2 ב
משרשי המצוה, לפי שהשם ברוך הוא חפץ ביישוב עולמו אשר ברא. ולכן ציוה לבל ישחיתו זרעם במשכבי הזכרים, כי הוא באמת השחתה שאין בדבר תועלת פרי ולא מצות עונה
The source of this commandment is that God desires the settlement of the world, which he created, and so he commanded [men] not to destroy their seed by intercourse with males, for this is indeed destruction. It effects neither offspring nor the fulfillment of the command to pleasure one’s wife (mitzvat onah). [Translation by Rabbi Steve Greenberg]
3 ג

Suggested Discussion Questions:

1. The social context of the Hinnukh here appears to be a man who destroys his seed by having sex with a male because it doesn't accomplish the twin goals of sexual relations, reproduction and the pleasuring of a legitimate partner. What do you make of this argument for the prohibition?

4 ד
Time Period: Medieval (Geonim through the 16th Century)