You shall utterly destroy all the places where the nations that you are dispossessing served their gods: on the high mountains and on the hills and under every leafy tree.
English: “And under every leafy tree” — And it is written there (Yeshayahu 57:5), “who console themselves with the elims under every leafy tree.” From here R’ Assi said: Anyone who emits seed in vain is as one who serves idolatry.
On the daf / in context: The parallel language in Yeshayahu links the site of idolatry with the practice of wasting seed; the derash equates the two in severity.
Type of Learning
Derash by parallel language (Sifrei) — equating the emission of seed in vain with idolatry.
What Is Learned
One who emits seed in vain is regarded as if he had served idolatry.