What was the disease of Job, peace be upon him? And what is the proof?

Muslims are in agreement regarding the humanity of prophets and the permissibility of illness and hunger befalling them. This has been affirmed by Quranic verses, such as Allah’s saying: ﴿ THE MESSIAH, SON OF MARY, WAS NOT BUT A MESSENGER; [OTHER] MESSENGERS HAD PASSED ON BEFORE HIM. AND HIS MOTHER WAS A WOMAN OF TRUTH. THEY BOTH USED TO EAT FOOD ﴾ [Al-Ma'idah: 75], and His saying: ﴿ SAY, "I AM ONLY A MAN LIKE YOU, TO WHOM HAS BEEN REVEALED THAT YOUR GOD IS ONE GOD" ﴾ [Al-Kahf: 110]. Ibn Taymiyyah reported the scholarly consensus that prophets may experience illness, hunger, and forgetfulness.

As for the illness of the Prophet Ayyub (Job), peace be upon him, the Quran did not detail its specifics, except that it was "distress and torment" from Satan, as in Allah’s saying: ﴿ AND REMEMBER OUR SERVANT JOB, WHEN HE CALLED TO HIS LORD, "INDEED, SATAN HAS TOUCHED ME WITH DISTRESS AND TORMENT." ﴾ [Sad: 41]. His tribulation was not a punishment, but rather for elevating his ranks due to his patience. Allah praised him by saying: ﴿ INDEED, WE FOUND HIM PATIENT, AN EXCELLENT SERVANT. INDEED, HE WAS ONE WHO OFTEN RETURNED [TO ALLAH]. ﴾ [Sad: 44].

Imam Ibn Kathir mentioned that Ayyub (peace be upon him) was afflicted in his body, wealth, and children, until nothing remained for him except his heart and his wife, who cared for him for eighteen years. After his supplication, Allah commanded him to strike the ground with his foot, and He caused two springs to gush forth: one for washing and the other for drinking, so he regained his health. Allah restored his family to him and twice their number with them. And because he had sworn to strike his wife one hundred lashes, Allah commanded him to take a bundle of thin stalks containing one hundred branches and strike her with it once, as an honor to her and to fulfill his oath. The lesson from his story is patience in the face of Allah's decrees and abundant obedience.