Malik said, "Someone who has a nosebleed on the day of jumuawhile the imam is giving the khutba and he leaves and does not comeback until the imam has finished the prayer, should pray four rakas.''Malik said that someone who prayed a raka with the imam onthe day of jumua, then had a nosebleed and left and came back and theimam had prayed both rakas, should complete the prayer with anotherraka as long as he had not spoken.Malik said, "If some onehas a nosebleed, or something happens to him and he has no alternativebut to leave, he does not have to ask permission of the imam if hewants to leave on the day of jumua."
USC-MSA web (English) reference: Book 5, Hadith 13