It is narrated from Sayyiduna Mu'awiyah bin Haydah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "In every herd of grazing camels, for every forty a bint labun (two-year-old she-camel) is due as zakah, and camels are not to be separated from their (collective) state. Whoever gives it seeking the reward will have its reward, and whoever withholds it, I will take it along with half of his wealth. This is one of the firm commands of our Lord. The family of Muhammad has no share in it."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17034