What does it mean that concubinage does not establish Ihsan for a slave-girl and her master?

Is it correct that there is a consensus that the chastity of a slave girl and her master is not established and even if she gives birth to children of her master unlike where chastity of husband and wife is established due to Nikah? [١٢٠/ ٢] التسري لا يحصل به إحصان للسيد، ولا إحصان للأمة. - موسوعة الإجماع في الفقه الإسلامي **(Note: I have provided heading only under which whole matter of ijma is discussed in the source)** Though In Qur'an Allah says > **And they who guard their private parts.** > > **Except from their wives or those their right hands possess, for indeed, they will not be blamed -** > - Surah Muminoon 5-6 Correct me If I understood it wrong