Sayyiduna al-Sa'ib bin Yazid (may Allah be pleased with him) said: I stayed in the company of Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him) for a period of time, and I heard only one hadith from him which he narrated from the Messenger of Allah (peace and blessings be upon him), that he (peace and blessings be upon him) said: "What is combined shall not be separated, and what is separate shall not be combined, in zakah. And 'partners' are those (whose animals) come together on the stud male, the trough and the shepherd."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7333