Hadith in the Majmu' Zayd about intercourse with underage slave girls

Asalam Alaykum Wa Rahmatullahi Wa Baraktuh 

I was reading through Musnad Zayd when I came across this ambiguous hadith. It says that whoever has sex with a minor-slave-girl will be responsible for it. What does this mean? Does this permit such an act or not? In the arabic it doesn't have the word Ehsan so I don't think it means liable for adultery punishment but alas I am a layman. May you please clarify? As I remember how you explained that the Zaydi fiqh prohibits such arrangements for pre-pubescents so I'm just hoping you could explain. 
wa alaykum as salaam wa rahmatullahi wa barakatuhu!

As for the narration in the Majmu', it basically translates into: "Whoever has intercourse with a girl under nine years old, is considered liable." The reason that I rendered the word jaariya as 'girl' and not 'slave girl' is because this narration appears in the chapter dedicated to issues of marriage. Therefore, the word 'girl' in this context may refer specifically to a girl with whom one has contracted a marriage. 

A similar narration--which may clarify the report in the Majmu'--appears in the Amaali Ahmed b. 'Isa in which the Commander of Believers (as) is narrated to have said: "Do not have intercourse with a girl under nine years old. Whoever does that and she is rendered impotent as a result, such one is considered liable." This liability therefore applies to compensation that he must pay due to the damage he caused to her. 

So, this may raise questions as to whether such liability exists for a girl over nine and whether one can have intercourse with a girl under nine years old. This is the reason why we must understand the narrations of our imams (as) through our imams (as)! 

As for the first question, I would say that Sayyid Imam Mansuur Billah al-Qaasim b. Muhammad (as) clarifies this in his Al-'Itisaam when he includes both narrations under the section heading "Deflowering one's wife." After quoting the narrations, he says: "This proves that the deflowering of one's wife who is not sound in body (as-saaliha) is subject to liability and that there is nothing due on the one who deflowers a woman sound in body due to her being conditioned to such (al-mu'taad)." The word mu'taad is derived from the Arabic 'awd, which indicates something sturdy, aged and experienced. This is also why Sayyid Imam Ibn al-Murtaza (as) says in his Al-Bahr: "There is nothing due on the one who deflowers the sound (as-saaliha) and conditioned (al-mu'taad) wife." Therefore, this shows that the soundness of a wife's body is a precondition of intercourse, not necessarily the age of nine. 

Sayyid Imam Mansuur Billah (as) goes on to say: "If he has intercourse with her outside of it (i.e. her body being conditioned) and she has incontinence of urine as a result, he owes compensation."

Sayyid Imam Mu´ayyad Billah (as) says in his Sharh at-Tajreed that the age of nine is not a precondition for one to have intercourse with one's wife. Rather, this is something determined by her puberty and soundness in body. We discussed this in detail in the footnotes of our translation of the Ahkaam. Furthermore, he says regarding how a woman's soundness in body is determined: "It is something that is known by women." The imam was not a feminist, but he knew that there are certain realms of knowledge reserved for women.

In conclusion, we say that the narration in the Majmu' possibly applies to a time when most women had not reached puberty and soundness in body before the age of nine. It is for this reason that he possibly set this age as a marker by which intercourse with wives does not render compensation. However, we know from the laws of compensation that any compensation for injury is not age dependent; therefore, it can be safe to say that it would even apply to a wife older than nine if she is not yet sound in body. We have a narration on the authority of Sayyid Imam Ja'far b. Muhammad as-Saadiq (as) from 'Ali, upon him be peace, passed a judgement that whoever struck another and it caused incontinence of urine or withholding of urine, must pay a third of compensation (Ref. Al-I'tisaam). This is irrespective of age. 

And Allah knows best!

IRS