Musnad Ahmad 686:1

Hushaym narrated to us, Hilal ibn Khabbab informed us, he said: Maysarah Abu Salih narrated to me, from Suwayd ibn Ghafalah, who said: The alms-collector (musaddiq) of the Prophet, may Allah bless him and grant him peace, came to us. He said: So I sat with him and I heard him saying: "Indeed, it is in my covenant that I shall not take from a suckling (animal), nor shall I combine that which is separate, nor shall I separate that which is combined." And a man came to him with a humpbacked she-camel and said: "Take it." But he refused to take it.