Muwatta Malik Book 5, Hadith 12
Yahya related to me from Malik that Ibn Shihab used to say, "Some
one who catches a raka of the jumua prayer should pray another one
with it." Ibn Shihab said, "That is the sunna."
Malik said,
"I saw the people of knowledge in our city doing that. That is because
the Messenger of Allah, may Allah bless him and grant him peace, said,
'Whoever catches a raka of the prayer has caught the prayer.' "
Malik said, concerning some one who was in a crowd on the day of
jumua and did the ruku but was not able to go into sajda until the
imam had risen or finished his prayer, "If he is able to do the sajda
and has already done the ruku then he should do the sajda when the
people stand up. If he is unable to do thesajda until after the imam
has finished the prayer, then I prefer that he begins the prayeragain
and does the four rakas of dhuhr."
Yahya related to me from Malik that he asked Ibn Shihab about talking in the jumua after the imam had come down from the mimbar but before he had said the takbir. Ibn Shihab said, "There is no harm in that."
Malik said, "Someone who has a nosebleed on the day of jumua while the imam is giving the khutba and he leaves and does not come back until the imam has finished the prayer, should pray four rakas.''
Malik said that someone who prayed a raka with the imam on the day of jumua, then had a nosebleed and left and came back and the imam had prayed both rakas, should complete the prayer with another raka as long as he had not spoken.
Malik said, "If some one has a nosebleed, or something happens to him and he has no alternative but to leave, he does not have to ask permission of the imam if he wants to leave on the day of jumua."