Musnad Ahmad 491:3

Abu al-Nadr narrated to us, Abd al-Hamid narrated to us, Shahr ibn Hawshab narrated to me, from Ibn Abbas, who said: "The Messenger of Allah, may Allah bless him and grant him peace, forbade certain types of women," and he mentioned the hadith. And he mentioned, attached to it, that he said: The Messenger of Allah, may Allah bless him and grant him peace, sat in a gathering, and Gabriel, peace be upon him, came and sat before the Messenger of Allah, may Allah bless him and grant him peace, and he mentioned the hadith. And he said in it: "If you wish, I will tell you of signs for it other than that." He said: "Yes, O Messenger of Allah, so tell me." And the Messenger of Allah, may Allah bless him and grant him peace, said: "When you see the slave-woman giving birth to her mistress," and he mentioned the hadith.