Musnad Ahmad 1302:7

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Yazid ibn Khumayr, who said: I heard ‘Abd al-Rahman ibn Jubayr ibn Nufayr narrating from his father, from Abu al-Darda’, from the Prophet (peace and blessings of Allah be upon him), that he passed by a pregnant woman at the door of a tent. The Prophet (peace and blessings of Allah be upon him) said: "Perhaps he intends to have intercourse with her?" They said: "Yes." The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have indeed considered cursing him with a curse that would enter his grave with him. How can he claim him as an heir when he is not lawful for him? How can he employ him as a servant when he is not lawful for him?"