It wasnarrated that Ka'b bin 'Ujrah said:
"The Prophet (ﷺ)commanded me, when I was suffering, from live, to shave my head andfast for three days or feed six poor persons. He knew that I did nothave an animal I could sacrifice." (IT)
English reference (IT): Vol. 4, Book 25, Hadith 3080 (IT)
Arabic reference (IT): Book 25, Hadith 3198 (IT)