Musnad Ahmad 2:137

I read to Yahya ibn Sa'id: Zuhayr, he said: Abu Ishaq narrated to us, from Harithah ibn Mudarrib: That he performed Hajj with Umar ibn al-Khattab. The notables of the people of Syria came to him and said: "O Commander of the Faithful, we have acquired slaves and beasts; so take from our wealth a charity by which you may purify us, and it shall be Zakat for us." He said: "This is something that the two who were before me did not do. However, wait until I ask the Muslims."