Musnad Ahmad 1013:41

Muhammad ibn Ubayd narrated to us, Muhammad ibn Ishaq and Ya’qub narrated to us, my father narrated to us, from Ibn Ishaq, Abbas ibn Sahl ibn Sa’d narrated to me, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said to ‘Asim ibn ‘Adi: "Keep her with you until she gives birth in your presence. If she gives birth to a red child, then he belongs to the father whom he (the husband) disowned, for ‘Uwaymir. But if she gives birth to a child with curly hair and a black tongue, then he belongs to Ibn al-Sahma’." ‘Asim said: When it happened, I took him to me. His head was like the fleece of a small lamb. Then I took—Ya’qub said: by his jaws—and he was reddish like the *nab’ah* wood, and his tongue met me, black like a date. He said: So I said, "Allah and His Messenger have spoken the truth."