Musnad Ahmad 980:9

Waki' narrated to us, Shu'bah narrated to us, from 'Adi ibn Thabit, from 'Abdullah ibn Yazid, from Abu Mas'ud al-Ansari, who said: The Prophet, peace and blessings of Allah be upon him, said: "A man's expenditure upon his family, while seeking reward for it, is charity."