Grading: Its chain is "sahih"
Note / Clarification: Ata is Ibn Abi Rabah.

Reference / Source: Abu Dawud (3954) and Ibn Hibban (4324) narrated it through two routes from Hammad bin Salamah, with this same chain.

Reference / Source: Imam Ahmad (22/ 14446), Ibn Majah (2517), al-Nasa'i (5021 and 5022) and Ibn Hibban (4323) narrated it through the route of Ibn Jurayj, who said: Abu al-Zubayr informed me that he heard Jabir bin Abd Allah say: We used to sell our slave-women and our umm walads (a slave-woman who has borne her master a child) while the Prophet (peace and blessings be upon him) was alive among us, and we saw no harm in it.

Technical note / Defect ('illah): Imam al-Bayhaqi says in "al-Sunan al-Kubra" (10/ 348): None of the routes mentions that the Prophet (peace and blessings be upon him) came to know of this act and approved them in it (that is, this is not a hadith of tacit approval).

Technical note / Defect ('illah): Imam Ibn Hazm says in "al-Muhalla" (9/ 219): There is nothing in it to show that the Messenger of Allah (peace and blessings be upon him) knew of it.

Reference / Source: It is established from Ali bin Abi Talib that he said: My view and the view of Umar agreed that the umm walads should not be sold, then later my view was that they may be sold; at this Abidah al-Salmani said: Your view and the view of Umar, held together with the community (in agreement), is dearer to me than your view alone, which brings division
Reference / Source: Abd al-Razzaq narrated it at (13224).

Important point: But it is established from Ali that in the end he withdrew from his view and adopted the view of Umar, as he said to Abidah al-Salmani and Shurayh: Judge as you used to judge, for I dislike disagreement, until the people are united in one community or I die as my companions died
Reference / Source: Imam al-Bukhari narrated it at (3707).

General principle: Imam al-Baghawi says in "Sharh al-Sunnah" (9/ 370): This shows that he agreed with the community on this issue, that they are not to be sold; and when a disagreement of the Companions ends in agreement and that era passes, it becomes "ijma'" (consensus).

Main discussion: (The editors say that) the claim of consensus is affected by the narration that Sufyan bin Uyaynah recorded in his "Juz'", in the recension of Zakariyya bin Yahya (19), from Amr bin Dinar from Ata bin Abi Rabah from Ibn Abbas: By Allah! Your umm walad is only like your sheep or your camel
Reference / Source: Imam al-Bukhari says in "al-Tarikh al-Kabir" (2/ 388) that this is the well-known fatwa of Ibn Abbas
Note / Clarification: Perhaps Ibn Abbas meant that during her master's lifetime her ruling is such that she does not have the rights of a free wife, nor do the consequences of marriage to a free woman apply (such as the limit of four wives), and Allah knows best.