[The particle of negation] (لا) in this ḥadīth—even though it is a negation of what comes after it—then its meaning is the prohibition of turning towards those affairs and being concerned with them, because they are not sound, in and of themselves. Rather, they are simply from the presumptions of the ignoramuses of the Arabs...

They used to believe that when the sick person mingled with the healthy, he would make them become sick and pass his disease to them. Likewise [did they believe] regarding camels. So the Prophet (صلى الله عليه وسلم) negated that and falsified it.