Musnad Ahmad 287:1

Isma'il ibn Ibrahim narrated to us, he said: Ayyub informed us, from 'Abdullah ibn Abi Mulaykah, he said: 'Ubayd ibn Abi Maryam narrated to me, from 'Uqbah ibn al-Harith, who said—and I heard it from 'Uqbah, but I am more mindful of 'Ubayd's narration—he said: I got married, and a black woman came to us and said: "I have breastfed both of you." So I went to the Prophet, peace and blessings of Allah be upon him, and said: "I married a woman, the daughter of so-and-so, and a black woman came to us and said: 'I have breastfed both of you,' and she is a liar." He turned away from me, so I came to him from the front and said: "She is a liar." He said: "How can you [keep her] when she has claimed that she has breastfed both of you? Leave her."