Musnad Ahmad 1165:10

'Affan narrated to us, Wuhayb narrated to us, he said: Ayyub narrated to us, from Salih Abu al-Khalil, from 'Abdullah ibn al-Harith, from Umm al-Fadl, she said: I came to the Prophet, peace and blessings of Allah be upon him, and said: "I saw in my dream, in my house or my chamber, a limb of your limbs." He said: "Fatimah will give birth, if Allah wills, to a boy, and you will nurse him." So Fatimah gave birth to Hasan, and she handed him to her, and she nursed him with the milk of Qutham. I brought him to the Prophet, peace and blessings of Allah be upon him, one day to visit him, and the Prophet, peace and blessings of Allah be upon him, took him and placed him on his chest. He urinated on his chest, and the urine reached his lower garment. I struck his shoulders with my hand, and he said: "You have hurt my son, may Allah rectify you," or he said: "May Allah have mercy on you." I said: "Give me your lower garment so I may wash it." He said: "The urine of a female infant is washed, and water is poured over the urine of a male infant."