Sexual intercourse with pre-pubescent slave girls

Can anyone please explain this hadith? Is this authentic? Zaid bin Hubab narrated to us from Hammad bin Salamah, from Iyas bin Mu'awiyah, regarding a man who bought a prepubescent slave-girl, do not those like her have sexual intercourse? He said, "There is nothing wrong with performing the sexual act upon her without observing Istibra." (Musannaf Ibn Abi Shaybah 16906, 16907)