Musnad Ahmad 30:2484

Yahya narrated to us, from Muhammad ibn ‘Amr, who said: Abu Salamah narrated to me, from Abu Hurairah, from the Prophet (peace and blessings of Allah be upon him), who said: "The owner of sick camels should not bring them to graze with the owner of healthy camels." And he said: "There is no contagion, no superstition, and no *hamah* (an owl or a bird of ill omen). So who infected the first one?"