Muwatta Malik #84

Yahya related to me from Malik from Yahya ibn Said that Said ibn al-Musayyab was asked, "What do you say about someone who is afflicted by a nose-bleed which does not stop? "Malik said that Yahya ibn Said said that Said ibn al Musayyab said, "I say that he should signal with his head." (i.e. instead of doing sajda or ruku.) Yahya said that Malik said, "That is what I like most out of what I have heard about the matter."