Longchenpa: masturbation

The ten unwholesome actions that produce falling from the higher realms into the lower ones, and nothing but suffering are as follows:

The three unwholesome actions of body

1. Cutting off life.
2. Taking what is not given.
3. Sexual transgression.

The four unwholesome actions of speech

1. Lying.
2. Divisive speech.
3. Sophistic speech.
4. Harsh words.

The three unwholesome actions of mind

1. Covetice.
2. Ill-will.
3. Wrong view.

c) The divisions,

i) The actions of body:

• Cutting off life is intentional killing of another
• Related is endangering life through beating and such.
• Taking what is not given is stealing another's goods.
• Related to this is getting them by using fraud.
• Transgressions in sex are with persons committed to others.
• Related are dharmas like improper sexual acts.

Everything from maliciously killing worms and insects, knowingly cutting off their lives, and striking them, chopping them up, and so forth is included in cutting off life.

Taking what is not given is stealing the wealth of others, and related is using fraud to have them given.

Sexual transgression, refers to another's spouse, those who are close relatives, or not in their right minds, or deliberately having sex at an improper place or time. Included are intercourse in forbidden parts of the body, such as the hands [masturbation].

The Abhidharmakosha says:

[1] Cutting off life [through waste of sexual energy], as we rightly think, is killing others.
[2] Taking what is not given [sex] makes another's wealth one's own;
[3] Including acquisition of it through force or deceit.
[4] Forbidden desires [homosexuality, adultery, etc], comprise the four kinds of wrongful sex.

The commentary on the Drowa Namje says [about sexual fantasy and masturbation]:

What is like the actual thing, is related to it.
Having arisen similarly, it is like it;
like beating someone with a stick and relying on magical ceremonies to that end.