Musnad Ahmad 240:0

Narrated to us by Yahya ibn Sa’id, from Shu’bah, who said: Narrated to us Qatadah, from Abu al-Maliḥ, from ‘Amr ibn Shas al-Aslami, who said: I was among those who went out with the Messenger of Allah (ﷺ) at the Battle of al-Hudaybiyyah. I was one of the people who had been struck by the fever, and I had a camel that I was riding. I said: "O Messenger of Allah, I am sick." He said: "Go, for you are excused." So I went, and I was among those who were excused.