Sunan Ibn Majah
3469
Sahih+3

It was narrated that Abu Hurairah said:“Mention of fever was made in the presence of the Messenger of Allah (ﷺ), and a man cursed it. The Prophet (ﷺ) said: ‘Do not curse it, for it erases sin as fire removes filth from iron.’”

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi