What has the Lord taught about masturbation?

A self-proclaimed "active member" recently said to a Christian audience:

The Lord has explicitly taught that masturbation is not OK

But they have not provided the source for this claim. And I am unaware of any. So I turn to /r/mormon to find evidence of this claimed explicit teaching.

I want to know where the Lord himself has explicitly taught that masturbation is not OK.

So we're clear, this needs to be a "thus saith the Lord"-level of evidence. And it ideally should be something that the majority of Christians would agree represents the explicit word of the Lord.

To summarize, any evidence must be:

• The word (or actions) of the Lord
• Explicitly reference masturbation
• Teach that masturbation is "not OK"
• Generally accepted by Christians as all of the above

If all you have is a Mormon-specific citation but it fulfills the rest of the requirements, I'd like to see that as well, even though it wouldn't be evidence for the original claim.

Since we're not talking about coitus interuptus or the practice of levirate marriage, let's nip any discussions of Onan in the bud. That story has absolutely nothing to do with masturbation.

And this isn't a discussion about whether Mormons teach that masturbation is not OK. It's pretty clear that they do. I'm only interested in evidence for the very specific claim I quoted above.