Musnad Ahmad 26:355

'Affan narrated to us, Mas'ud ibn Sa'd narrated to us, Khasif narrated to us, from Abu 'Ubaydah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) wrote regarding the Zakat of cattle: "When the cattle reach thirty, there is due upon them a *tabi'* (a one-year-old calf) of cattle, a *jadha'* (male) or a *jadha'ah* (female), until they reach forty. When they reach forty, there is due upon them a *musinnah* (a two-year-old cow). When the cattle increase, then for every forty cattle, there is a *musinnah*."