Musnad Abu Ya'la al-Mawsili 150:64

Muhammad ibn Abdullah ibn Numayr narrated to us, Muhammad ibn Khalid ibn 'Athmah narrated to us, from Abdullah ibn Munib, from Hisham ibn Urwah, from his father, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "It is not lawful for a Muslim to forsake his brother for more than three [days]."