It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "There is no zakah on working cattle; but on every thirty, a one-year-old calf, and on every forty, a two-year-old cow or bull (is to be given in zakah)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10928